Use new MacMini slaves
Use new MacMini slaves

BUG=556703

Review URL: https://codereview.chromium.org/1470003002

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