NFS/GlusterFS: Skip incorrectly formatted shares

Shares should always be of the form address:/volume.  If they are
not (i.e., are missing the '/'), then skip them and issue a warning
message.  This will prevent us from sending incorrect connection_info
dicts to Nova.

Closes-Bug: #1267253

Change-Id: Ic40cd0cdc862b44b0a7d3e5b1d7c4fee8ea1b28d