Add master=tryserver.skia to RietveldPoller's endpoint.
Add master=tryserver.skia to RietveldPoller's endpoint.

BUG=skia:2659
TBR=borenet@google.com

Review URL: https://codereview.chromium.org/323353002

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