Fail the RPC when we fail to de-serialize its response.

Whenever we fail to de-serialize the response to an RPC, we throw an
exception that is caught by Netty, which then causes us to go into
exceptionCaught(), from which we ought to close the connection to HBase
and cleanup() all outstanding RPCs (either by re-scheduling them if we
can, or by making them fail with a ConnectionResetException).

This change will make the error a bit more explicit for the RPC that
initially failed to be de-serialized, while the other ones will seem
to fail due to a connection being reset.