Fix race in verify_capabilities

We wait until rings are ready, but the capability server is notified
asynchronously through riak_core_ring_events:ring_update and we were
sometimes querying the capability too soon. Now uses wait/retry logic.
Also, removing sleep timers from cap server restart. Now using
wait/retry also to detect a new cap server process.
Merge pull request #140 from basho/eas-fix-verify-capabilities

Fix Capabilities test failure