Add --stopbefore for easier simul-pushes.
Remove "--shuffle" from the example deploy.

It's not really necessary in reddit.com usage anymore because the hosts
are shuffled already by virtue of the autoscaler.
Fix SSH connection caching.

Turns out that it was always recreating the connection every single time
which is very wasteful when you do a half dozen actions on a single host
in quick succession. Oops.

A test of a deploy similar to a common-case "-pc -dc -r all" with ~280
servers showed total deploy time going from 17 to 6.5 minutes. In the
prior case 10 minutes in total were spent waiting on connection
establishment and after the patch that drops to 94 seconds.
Find host to start at before processing loop

This is mainly to prevent harold from spamming up IRC with progress
notifications when you restart an interrupted push that's already past
some notification points.
move stop_before outside as well