Improvements to gluster integration

Some various execution module improvements:
 * Dig is no longer required
 * list_peers now returns None for empty lists instead of ['No peers present']
 * simplified peer probe
 * rewrote create to follow the syntax and options in gluster
  * previous version required same brick path on all hosts
 * rewrote status to provide a useful structure of services running for requested volume
 * improved start_volume and added stop_volume and delete calls

State module improvements:
 * modified to work with changes in execution module
 * start parameter in created will now ensure the volume is started
  * before it would only start at creation
 * cleaned some of the output data structures

Whew!