Add missed discoverable policy rules for flavor-manage v3

Add discoverable policy rule for v3 extension flavor-manage,
Although without this patch, it also works. But that's used to
indicate to user there is option for flavor-manager discoverable.

Change-Id: I23f8bbaccfa104a12e4a4c9eea8bf04107b57d43
Migrate test_glance from mox to mock

A few tests in test_glance.py are still using mox. Update these
remaining tests to use mock, as this is the general direction in
which the project is moving.

Change-Id: I81fc36467b158625f29593c7173542f843244311
Add expire reservations in backport position.

Change-Id: If0e58da50ebe9b50b414737a9bd81d93752506e2
Related-bug: #1348720
Merge "Add missed discoverable policy rules for flavor-manage v3"
Merge "Add expire reservations in backport position."
Merge "Migrate test_glance from mox to mock"