impossible to catch 'all job servers fail' error

[dcolens]

The error 'all job servers fail' is thrown before the job is returned making it impossible for a client app to catch it. in the scenario where all servers are temporarily invalid, line https://github.com/veny/GearmaNode/blob/8ad6e4895cae315b58a942b00d982d4b6bd48f4d/lib/gearmanode/client.js#L165 triggers before line https://github.com/veny/GearmaNode/blob/8ad6e4895cae315b58a942b00d982d4b6bd48f4d/lib/gearmanode/client.js#L172.