Fix coerce good values in test_fields.py
Fix coerce good values in test_fields.py

In another patch, working on making Volume Attach Status into an
enum, it was pointed out that the way values were being tested. This
patch goes back and fixes how the other status fields are coercing
good values.

Change-Id: I33c0308ac97a31c3907af3c459eb0cb55e2d7a51

NetApp/cinder,Nexenta/cinder,mahak/cinder,Datera/cinder,cloudbase/cinder,openstack/cinder,NetApp/cinder,phenoxim/cinder,Hybrid-Cloud/cinder,Hybrid-Cloud/cinder,eharney/cinder,Nexenta/cinder,Datera/cinder,phenoxim/cinder,ge0rgi/cinder,cloudbase/cinder,eharney/cinder,mahak/cinder,openstack/cinder,j-griffith/cinder,j-griffith/cinder