Rename cinder.flags to cinder.common.config

Replace FLAGS with cfg.CONF
Rename modules fake_flags to conf_fixture, test_flags to test_conf, declare_flags to declare_conf, runtime_flags to runtime_conf
Renamed cinder.flags, because exactly the same was done in the glance and nova

Fixes: bug #1182037
Change-Id: I3424d0a401b3ef7a3254d3e913263554361a52ff
Merge "Rename cinder.flags to cinder.common.config"