Bug 1055793 - Use runner on OS X; r=rail

Installs runner along with a launchd init config in relatively unchanged fashion from Linux hosts.
Backed out changeset 1b661c1ac582

This changeset, while fine on the surface, changes the buildslave environment in ways
that break jobs.
Bug 1055793 - Ensures that runner.plist is absent from OSX hosts

In the event that a change to runner requires a rollback, this will prevent the runner launchd config
from causing problems.
Bug 8516404 - Pin test and build nodes to my environment in scl3; a=nodechange
Bug 1095160 - Run add_swap before runner. r=catlee