Hypervisor should re-establish transports after restart

[jdknives]

Feature description

After shutting down and restarting the hypervisor, it should attempt to re-establish dmsg streams to the visors that have previously been connected to it.

Is your feature request related to a problem? Please describe.
When restarting a hypervisor, it does not establish dmsg streams to the visors previously connected, so a user would have to manually re-establish the connections, which comes with its own problems.

Describe the solution you'd like
The hypervisor could store the PubKeys fo the visors connected. After a restart, it should try to establish a new dmsg stream to them again once.

[jdknives]

Also, when the dmsg.Server crashes and comes back up, the session is re-established successfully on both sides (visor and hypervisor) but the stream between visor and hypervisor is not re-established and therefore no commands can be called from the hypervisor. This will need to be fixed. A restart fixes that, but the restart endpoint cannot be called without a connection, assuming we do not have access to node itself.