Adding Volume API Unit test case.
Adding Volume API Unit test case.

Signed-off-by: Ram Suradkar <77c7960e890deddebb7ff2e55e340d2ed1708368@infracloud.io>

libopenstorage/openstorage,pault84/openstorage,libopenstorage/openstorage,pault84/openstorage,pault84/openstorage,libopenstorage/openstorage