migrate to os-api-ref

os-api-ref is released now, so we can move to using it instead
of copy pasting in cinder tree.

Change-Id: Id38dd0609c77b0d6bcd0d935a9312b0211134802

test-requirements.txt

@@ -11,6 +11,7 @@ ddt>=1.0.1 # MIT
 fixtures<2.0,>=1.3.1 # Apache-2.0/BSD
 mock>=1.2 # BSD
 mox3>=0.7.0 # Apache-2.0
+os-api-ref>=0.1.0 # Apache-2.0
 oslotest>=1.10.0 # Apache-2.0
 sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2 # BSD
 python-subunit>=0.0.18 # Apache-2.0/BSD