Enhance tests for flavor_extra_spec API

1) Test for GET {flavor_id}/os-extra_specs/{key_id}
2) Add a negative test to test extra spec key update

Change-Id: I0d424005586f0bcc27642fa9124c7e35a99f8724
Add test for update/reset_snapshot_status API

Add some tests fot update/reset_snapshot_status API

Change-Id: I5131ab1bdf3541bb139efd4ef4be5cd37e8f2774
Merge "Add test for update/reset_snapshot_status API"
Merge "Enhance tests for flavor_extra_spec API"