Serialize index creation/removal through claimant

Currently Yokozuna has data race issues when modifying the index list
on disjoint nodes.  For example the `yz_index_admin` test would lose
indexes (for a purely additive test, i.e. no index removals) without
sleeps in the right places to allow ring gossip to occur.  This patch
sidesteps the issue by forcing all Yokozuna index ring updates to be
applied at the claimant.  Forcing all updates to serialize on one
node.

If the claimant is down then index addition/removal cannot occur.
Just like with node addition/removal.  I think this is an acceptable
tradeoff for index addition/removal.  You probably shouldn't be
changing indexes when the cluster is in a bad state anyways.
Check for `rpc_fail` during index creation

Check for `rpc_fail` in index HTTP resource and return 500.
Fix typo
Merge branch 'master' into rz-ring-race

Conflicts:
	src/yz_misc.erl

Functions were added to same place in `yz_misc` on master and
rz-ring-race.  Kept all functions.
Merge pull request #128 from basho/rz-ring-race

Serialize index creation through claimant