When receiving ServerNotRunningYetException, a client shouldn't retry to
send the request to the same server. Instead, the client should be
closed and the region lookup should happen again.

There is two cases when ServerNotRunningYetException is returned:
- when the RegionServer is listening but not online yet: in that case,
  retrying the RPC on the same server may succeed if the Regionserver
  become ready and if the region is indeed assigned to it. But most
  likely the region would have been reassigned to another Regionserver
  and thus it will return NotServingRegionException in the following
  request. If the Regionserver is stuck in startup phase, it could also
  cause the client to be stuck in retry loop whereas HBasemaster may
  have detected the issue and correctly moved the region to another
  Regionserver already.

- when the HBasemaster server is currently not active: in that case,
  retrying the RPC on the same server is guaranteed to fail until a
  failover. The client will be stuck in a forever retrying loop.

If we receive multiple ServerError for the same RPC, we will backoff
before retrying. This is to avoid overwhelming HBase. Scenario where
this could happen is a cluster that is recovering from catastrophic
failure, with all HBasemaster still trying to start (like recovering
WALs or what not).

Also add MasterStoppedException and PleaseHoldException to the list of
known exception that can be returned by HBase.

Fix #265