restapi: Support for gluster hooks added

Gluster hooks are deployed during installation of gluster
in the servers of a gluster cluster. The ovirt engine polls
each of the servers in the cluster and stores information
about the gluster hooks - primarily to check if the hook
scripts are in sync across servers.

This patch adds API support for managing gluster hooks.
 - api/cluster/{id}/glusterhooks
   lists all gluster hooks in the cluster along with
   conflict status
 - api/cluster/{id}/glusterhooks/{glusterhook:id}|rel=delete
   resolve missing hook conflict by removing hook script from
   all servers and engine database
 - api/cluster/{id}/glusterhooks/{id}
   show details of a gluster hook

    actions supported:
        - enable
          enables hook in all servers in the cluster
        - disable
          disables hook in all servers in the cluster
        - resolve
          action.resolutionType = COPY
          resolve content conflict by copying content from either
          engine or from one of the servers to all or servers where
          the hook is missing as applicable (based on parameters)
          action.resolutionType = ADD
          resolve missing hook conflict by copying hook stored in
          engine database to all servers where the hook is missing

Change-Id: Ibf9c0299977448e0b50feeed6e38a015c60b86fd
Signed-off-by: Sahina Bose <sabose@redhat.com>