Update rename_node to also set claimant field.
Update rename_node to also set claimant field.

If reip is being used to restore a dead cluster and the previous
claimant node is renamed first then the ring never converges (see below).
This change modifies rename_node to also check the claimant field
and update as necessary.  The ring manager / claimant could also
be hardened to verify the claimant is a valid node in the cluster,
but I suspect that will be worked with riak_ensemble in the near future.

Example with previous claimant dev1 renamed to dev4

red:dev john$ dev1/bin/riak-admin ring-status
================================== Claimant ===================================
Claimant:  'dev1@127.0.0.1'
Status:    down
Ring Ready: unknown

============================== Ownership Handoff ==============================
No pending changes.

============================== Unreachable Nodes ==============================
The following nodes are unreachable: ['dev1@127.0.0.1','dev2@127.0.0.1',
                                      'dev3@127.0.0.1']

WARNING: The cluster state will not converge until all nodes
are up. Once the above nodes come back online, convergence
will continue. If the outages are long-term or permanent, you
can either mark the nodes as down (riak-admin down NODE) or
forcibly remove the nodes from the cluster (riak-admin
force-remove NODE) to allow the remaining nodes to settle.
red:14bb045be07a46bd37752974df2d123029e93ded@127.0.0.1
Failed: d23e16e39d49e9335c582fd13c0f3f4c47621e0a@127.0.0.1" is not a member of the cluster.

Kyorai/riak_core