Add a salt runner that safely accepts minion keys using salt-ssh

With the creation of salt-ssh, preseeding minions is no longer the only automated way to safely get connected with the master. I added a reference implementation of a salt-run function that uses salt-ssh to check the fingerprints of the minion keys and then, if they match, accepts them on the master.

Potential use case:
1) launch server with your cloud provider's api
2) update your roster
3) salt-run manage.bootstrap myserver
4) salt-run manage.safe_accept myserver

Even if it doesn't get merged, I thought the concept and code might be useful.