When a retryable error is encountered, the region is unavailable
When a retryable error is encountered, the region is unavailable

In the event of a retryable error, we were blindly resending the RPC. We
want to mark the region as unavailable. This differs from an
unrecoverable error because in this case the region client is not dead,
and all other regions sharing the client are probably fine.

Change-Id: I16b21c5bf76a7f6d710047fa410b32c532854df6

tempbottle/gohbase,dougklein/gohbase,dougklein/gohbase,tsuna/gohbase