Implement cluster admin RPCs to change member voting states

Implement cluster admin RPCs to change member voting states

Backported from master: https://git.opendaylight.org/gerrit/#/c/38086/

Added 3 new RPCs for changing voting states:
  change-member-voting-states-for-shard
  change-member-voting-states-for-all-shards
  flip-member-voting-states-for-all-shards

These replace the original ones added in Be that weren't implemented.
They were added as placeholders based on how it was thought it would
work at that time.

New related ShardManager messages were added that are sent by the
ClusterAdminRpcService.

The flip-member-voting-states-for-all-shards RPC is a shortcut that
obtains the current voting states via the GetOnDemandRaftState message
to the RaftActor and inverts them. New fields were added to the
OnDemandRaftState response to return the voting states.

Modified the ShardStats JXM bean to report the new OnDemandRaftState
fields.

Added a check in RaftActorServerConfigurationSupport to ensure that
there's at least 1 voting member otherwise one can end up with an
unusable shard with no ability to elect a leader.

Fixed a couple bugs in Leader and AbstractLeader that were found during
testing. AbstractLeader needs to take into account the follower's voting
state when determining if the leader is isolated.

Change-Id: I58686e3ce94d58de7cf289e55bb717ba46bc1de5
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>