cmake: clean up on successful runs and randomise test scheduling (#202)

In the case where we create the test path, we should clean up after the
run finishes as done in the Makefile, due to garbage that is left behind
by tests and accumulates.

While at it, randomise test scheduling in order to increase the likelihood
of surfacing latent bugs that are hidden by the execution order.

cmake/CTestRunner.cmake

@@ -110,4 +110,9 @@ else()
 endif()
 
 # Run all tests, and show test output on failure
-execute_process(COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure --timeout ${test_timeout})
+execute_process(COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure --schedule-random --timeout ${test_timeout} RESULT_VARIABLE rv)
+
+# Clean up after ourselves if the run was successful
+if(DEFINED tmpdir AND DEFINED rv AND ${rv} EQUAL 0)
+    file(REMOVE_RECURSE ${tmpdir})
+endif()