fix regexp for bash userdata

[angel-manuel]

Some may use user-data scripts like the following one.
Don't capture the quotes with the regexp

echo "ECS_CLUSTER=core-dev" >> /etc/ecs/ecs.config

[taraspos]

@angel-manuel thanks for your contribution.

I know there are no tests for the lambda yet, but this like a good place to start adding them.
Could you do that?

Basically, move following lines into a separate function:

ecs-drain-lambda/ecs.go

Lines 177 to 182 in c7c20f8

	// Using RegExp to get actual ECS Cluster name from UserData string
	m := ecsRegExp.FindAllStringSubmatch(string(decodedUserData), -1)
	if len(m) == 0 || len(m[0]) < 2 {
	fmt.Printf("UserData:\n%s", string(decodedUserData))
	return "", ErrMissingECSClusterInUserData
	}

And add tests with a couple of different UserData examples.

[taraspos]

Merged in #9