keeper: wait for updated ip to appear in keepersState view.

[sgotti]

At startup the keeper should wait for its updated ip to appear in the store's keeperState view.

This will fix a very uncommon and strange case where a standby keeper is reconfigured with the ip of the master keeper AND the sentinels are down (#154).

[sgotti]

This is fixed in #200. We don't directly check the db listenaddress:port (keeper doesn't listen anymore) but a bootUUID fields that is generated at every keeper restart. So when the new bootUID is reflected in the cluster data we can assume that also the pg listenaddress and port have been updated.