Switch to private IPs for Mac VMs for now
Switch to private IPs for Mac VMs for now

There's a firewall issue causing the workers to connect to VMs when they
are being run on the VM host. Once the workers are being moved off the
VM host we can switch back to public IPs.

travis-ci/travis-worker,ireznice/travis-worker,final-ci/travis-worker,travis-ci/travis-worker,final-ci/travis-worker,ireznice/travis-worker,gavioto/travis-worker,gavioto/travis-worker