Fix failing tests on WSME 0.5b6 (failing CI)

The failures had two parts:

* The namespace of errorneous response doesn't contain 'result' key
  anymore, so we have to check for 'faultcode' first and render error
  immediately, before we look for 'result'.

* New WSME has stricter validation and some resources in the tests
  don't pass that. It looks like WSME did not enforce mandatory=True.
  Now it does. Changed to mandatory=False for field "id" in Flavor type
  in tuskar/api/controllers/v1/types/flavor.py b/c we do not need incoming
  request to contain id in body when creating/updating Flavor.

Fixes-Bug: #1240934
Change-Id: I6a5764a852fd81bc56814840af38a357b7f97d40