DETACHED with error still means detached, not failed

[paddybyers]

I’m running the deploy-cores-with-lots-of-active-channels test, and under load we get some channels being detached, which results in a DETACHED message with error sent to the client.

However, in ably-js we then transition to failed instead of detached:

Ably: Transport.onProtocolMessage(): received on web_socket: [ProtocolMessage; action=DETACHED; channel=testchannel923; error=[ErrorInfo: Master retired/disabled; statusCode=400; code=40000]]
Ably: Channel state for channel "testchannel923": failed; reason: Master retired/disabled, code: 40000

[SimonWoolf]

Fixed by #313