respect --os-version and --os-type in teuthology.run

This should fix issue #10279.  I tested in octo and sepia with a yaml config that included os_type and os_version and ensured that --os-type and --os-version will override what's in the yaml if used.  I also test with a config that did not include os_type or os_version.  I tested with vps machines in sepia and bare metal in octo.

Passing runs using this branch:

http://pulpito.ceph.redhat.com/andrewschoen-2014-12-16_16:49:17-rest-giant-distro-basic-magna/
http://pulpito.front.sepia.ceph.com/ubuntu-2014-12-17_07:27:24-rest-giant-distro-basic-vps/
http://pulpito.front.sepia.ceph.com/ubuntu-2014-12-17_09:47:51-rgw-dumpling-testing-basic-vps/ (test failures are unrelated to this branch)

Also, if you compare runs of rgw you'll see that this branch fixes a bug that was causing dead jobs as well.

http://pulpito.front.sepia.ceph.com/compare/?branch=dumpling&suite=rgw