Handle missing flavor.id in server response

Change Ie2d57029ad01cbe9e2b015857d6b95f77a97be19 introduced checks
for a servers flavor ID. This data is no longer returned after
Nova API microversion 2.46, causing problems for any tests/clients
requesting a higher version number.

Since these tests are not concerned with validating flavors, just
check if it is returned in the base class and skip the check if
it is not available.

Change-Id: Id7760cdfb9874014e03c7d8ebe269a03562bde18
Closes-bug: #1744401
1 file changed