PWX-5813: Use const for time format.
PWX-5813: Use const for time format.

Signed-off-by: Jose Rivera <4a3487e57d90e2084654b6d23937e75af5c8ee55@portworx.com>

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