Support for UBNT EdgeMax PoE via. rancid

[sjthespian]

I have a new UBNT EdgeMax switch, so cloned my Cisco Rancid code to also support this switch. I will be submitting a PR with my new code in a few minutes.

One thing to be aware of, if the ssh connection to the switch hangs, it will hang requests to powerman. I haven't found a good way around this. One fix is to use a shorter timeout in the rancid command, but that will cause powermand to reconnect to the switch every time the timeout expires.