Salt Raet now allows the master to reboot and will rejoin with minions

Added preliminary support for presence in Salt on RAET.
Needs Raet 0.0.24

Master now has behavior thate manages keep alive messages to minions
This was added to salt's ZMQ event class because we had to manually close/destroy the sockets or we would leak threads. If you that such destroy procedure is not necessary with raet, you could probably omit it?