Add ping_quorum and get_peer_info support calls

riak_ensemble_peer:ping_quorum/1 checks an ensemble for an active
quorum, returning the current ensemble leader as well as the list of
peers supporting the current quorum.

riak_ensemble_manager:get_peer_info/2 returns information about a
given ensemble peer: the peer's current FSM state, if it is or is not
trusted, and it's current epoch.
Merge pull request #26 from basho/feature/ensemble-commands

Add ping_quorum and get_peer_info support calls

Reviewed-by: engelsanchez