Fix disconnect/reconnect issues

Fix disconnect/reconnect issues

Commit 155d78b39933a396d2555376f4e70f976c30b86d prevented reconnections
from working properly.  This fixes that by creating a new RFB object
after disconnecting or failing.

Furthermore, this ensures that a new connection cannot be opened util
we've actually disconnected (either by timer or by receiving a `close`
event).

Closes #452