Add buildslave for NVIDIA Shield on Mac Mini
Add buildslave for NVIDIA Shield on Mac Mini

...because the existing hosts are overloaded, and I want to see what
happens.

BUG=skia:3916

Review URL: https://codereview.chromium.org/1163323002

google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot