Have setup_ubuntu script check for MAC_PAUSE
Have setup_ubuntu script check for MAC_PAUSE

Ansible has the ability to run steps conditionally using when:
http://docs.ansible.com/ansible/latest/playbooks_conditionals.html

Bug: skia:6815
Change-Id: I806ec02adaa6f2520421faa150fdc1db1cf50847
Reviewed-on: https://skia-review.googlesource.com/28700
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Commit-Queue: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot