Revert of Poll Rietveld every 15 mins instead of every min. (https://codereview.chromium.org/333643003/)
Revert of Poll Rietveld every 15 mins instead of every min. (https://codereview.chromium.org/333643003/)

Reason for revert:
Going back to polling every 1 min.

Original issue's description:
> Poll Rietveld every 15 mins instead of every min.
>
> BUG=skia:2659
> TBR=borenet@google.com
>
> Committed: https://skia.googlesource.com/buildbot/+/758b93d

R=borenet@google.com
TBR=borenet@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:2659

Author: rmistry@google.com

Review URL: https://codereview.chromium.org/335813002

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