[Resolve Sceptre#1483] Handle errors in change sets

This adds code to handle the case of failures in stack groups that have
missing or errored stacks when creating, describing and executing
change-sets.

Before this, any stack group that contained a stack that had been
deleted, or had errored out, resulted in all change set operations on
that stack group failing.

The reason for this is no error or exception handling had ever been
added for change sets, but assumed all stacks in the stack group were
clean and could respond to the change set APIs.

For example, deleting change sets might error out with:

```
% sceptre delete -y network.yaml sceptre-network
The Change Set will be delete on the following stacks, if applicable:
network

"An error occurred (ValidationError) when calling the DeleteChangeSet
operation: Stack [test-e2e-direct-connect] does not exist"
```

This is particularly an issue for sites that employ as best practice
analysis of change sets for safety prior to launching updates.

This patch adds the missing error handling for `delete_change_set`,
`create_change_set`, `describe_change_set` and
`execute_change_set`.

sceptre/cli/helpers.py

@@ -337,6 +337,9 @@ def simplify_change_set_description(response):
     :returns: A more concise description of the change set.
     :rtype: dict
     """
+    if not response:
+        return {"ChangeSetName": "ChangeSetNotFound"}
+
     desired_response_items = [
         "ChangeSetName",
         "CreationTime",

sceptre/plan/actions.py

@@ -465,8 +465,24 @@ def create_change_set(self, change_set_name):
                 {"Key": str(k), "Value": str(v)} for k, v in self.stack.tags.items()
             ],
         }
+
         create_change_set_kwargs.update(self.stack.template.get_boto_call_parameter())
         create_change_set_kwargs.update(self._get_role_arn())
+
+        try:
+            self._create_change_set(change_set_name, create_change_set_kwargs)
+        except Exception as err:
+            self.logger.info(
+                "%s - Failed creating Change Set '%s'\n%s",
+                self.stack.name,
+                change_set_name,
+                err,
+            )
+
+    def _create_change_set(self, change_set_name, create_change_set_kwargs):
+        """
+        Wrap create_change_set.
+        """
         self.logger.debug(
             "%s - Creating Change Set '%s'", self.stack.name, change_set_name
         )
@@ -490,6 +506,27 @@ def delete_change_set(self, change_set_name):
         :param change_set_name: The name of the Change Set.
         :type change_set_name: str
         """
+        # If the call successfully completes, AWS CloudFormation
+        # successfully deleted the Change Set.
+        try:
+            self._delete_change_set(change_set_name)
+            self.logger.info(
+                "%s - Successfully deleted Change Set '%s'",
+                self.stack.name,
+                change_set_name,
+            )
+        except Exception as err:
+            self.logger.info(
+                "%s - Failed deleting Change Set '%s'\n%s",
+                self.stack.name,
+                change_set_name,
+                err,
+            )
+
+    def _delete_change_set(self, change_set_name):
+        """
+        Wrap delete_change_set.
+        """
         self.logger.debug(
             "%s - Deleting Change Set '%s'", self.stack.name, change_set_name
         )
@@ -501,13 +538,6 @@ def delete_change_set(self, change_set_name):
                 "StackName": self.stack.external_name,
             },
         )
-        # If the call successfully completes, AWS CloudFormation
-        # successfully deleted the Change Set.
-        self.logger.info(
-            "%s - Successfully deleted Change Set '%s'",
-            self.stack.name,
-            change_set_name,
-        )
 
     def describe_change_set(self, change_set_name):
         """
@@ -518,6 +548,21 @@ def describe_change_set(self, change_set_name):
         :returns: The description of the Change Set.
         :rtype: dict
         """
+        return_val = {}
+
+        try:
+            return_val = self._describe_change_set(change_set_name)
+        except Exception as err:
+            self.logger.info(
+                "%s - Failed describing Change Set '%s'\n%s",
+                self.stack.name,
+                change_set_name,
+                err,
+            )
+
+        return return_val
+
+    def _describe_change_set(self, change_set_name):
         self.logger.debug(
             "%s - Describing Change Set '%s'", self.stack.name, change_set_name
         )
@@ -543,16 +588,30 @@ def execute_change_set(self, change_set_name):
         change_set = self.describe_change_set(change_set_name)
         status = change_set.get("Status")
         reason = change_set.get("StatusReason")
-        if status == "FAILED" and self.change_set_creation_failed_due_to_no_changes(
-            reason
-        ):
+
+        return_val = 0
+
+        if status == "FAILED" and self._change_set_failed_no_changes(reason):
             self.logger.info(
                 "Skipping ChangeSet on Stack: {} - there are no changes".format(
                     change_set.get("StackName")
                 )
             )
-            return 0
+            return return_val
+
+        try:
+            return_val = self._execute_change_set(change_set_name)
+        except Exception as err:
+            self.logger.info(
+                "%s - Failed describing Change Set '%s'\n%s",
+                self.stack.name,
+                change_set_name,
+                err,
+            )
+
+        return return_val
 
+    def _execute_change_set(self, change_set_name):
         self.logger.debug(
             "%s - Executing Change Set '%s'", self.stack.name, change_set_name
         )
@@ -567,7 +626,7 @@ def execute_change_set(self, change_set_name):
         status = self._wait_for_completion(boto_response=response)
         return status
 
-    def change_set_creation_failed_due_to_no_changes(self, reason: str) -> bool:
+    def _change_set_failed_no_changes(self, reason: str) -> bool:
         """Indicates the change set failed when it was created because there were actually
         no changes introduced from the change set.