Investigate implementation of RTN15a

[funkyboy]

https://docs.ably.io/client-lib-development-guide/features/#RTN15a says
"If a Connection transport is disconnected unexpectedly or if a token expires, then the Connection manager will immediately attempt to reconnect and restore the connection state."

Looking at the current implementation it seems like connection retries are always timer based and the first is not tried right away.

Some discussion here #726 (comment)

[ricardopereira]

@mattheworiordan Is this the bug (does not retry a connection when it fails immediately, it waits 15s now) that you talked about?

[mattheworiordan]

Yes

[ricardopereira]

@funkyboy Paddy told me that you will handle this, is that right?

[funkyboy]

Fixed in #789