Extract failure reason before deleting nova server

If a nova server create fails, the server is deleted
leaving no indication of the source of the failure.

This change extracts the failure reason from the nova
server fault attribute and includes that in the raised
error.

Change-Id: I7a4618d9e3fded3cde1c15d5322b52eaf63a68f5
Merge "Extract failure reason before deleting nova server"