Moto's implementation of autoscaling:CreateLaunchConfiguration is a little too loose,
allowing the ImageId parameter to be omitted and defaulting it to None, which results
in dozens of deprecation warnings:
`PendingDeprecationWarning: Could not find AMI with image-id:ami-123456, in the near future this will cause an error.`
This commit refactors calls to CreateLaunchConfiguration to explicitly pass in a known
AMI ImageId in order to avoid these warnings.
The integrity of the tests is unaffected by this change.
