gluster: Added verbs for read, update, add and remove hooks

Below new verbs are added to perform read, update, add and remove hooks

* hookRead
  Output Structure:
       {'content': HOOK_CONTENT,
        'type': MIME_TYPE,
        'md5sum': MD5SUM}
* hookUpdate
* hookAdd
* hookRemove

Change-Id: Ie123356209aa0f71176bd06b9c53e0e96211e716
Signed-off-by: Timothy Asir <tjeyasin@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/14145
Reviewed-by: Aravinda VK <avishwan@redhat.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>