Fix bench_pictures slave-side script: _revision -> _got_revision
Fix bench_pictures slave-side script: _revision -> _got_revision

BUG=skia:2714
R=kelvinly@google.com, bensong@google.com
TBR=bensong, kelvinly

Author: borenet@google.com

Review URL: https://codereview.chromium.org/367013002

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