Handle a flavor create failed better

Catch FlavorCreateFailed exceptions which when flavor creation fails.
This type of flavor creation failure is caused by an internal nova problem.
Return an internal server error (500) to the user so they know
to contact their cloud provider.

Closes-Bug: #1292309

Change-Id: I268c84dae290b0170448d789509af781555df9b0
Merge "Handle a flavor create failed better"