gluster: VDS command to fetch gluster services

- VDS Command
- VDS Parameters class
- XmlRpc return type
- Entries in VDSCommandType, IVdsServer, VdsServerConnector, VdsServerWrapper
- New error code in VdcBllErrors and VdsmErrors
- New enum for service statuses (GlusterServiceStatus)
- Refactored ServiceInfo to use GlusterServiceStatus instead of
  GlusterStats

Change-Id: I0c59a6f153fdcb584de206ca389a2ef7ce30fd80
Signed-off-by: Shireesh Anjal <sanjal@redhat.com>