influxdb/grafana: Add parsing for tags.
influxdb/grafana: Add parsing for tags.

This should reduce the total number of measurements we have in influxdb, which seems to be problematic for Grafana.

Will need to drop and recreate the database after this lands to clean out the old measurements.

Should also only land after https://codereview.chromium.org/1393883002 (Fix: logserver and pulld were double reporting their hostname.) lands.

BUG=skia:

Review URL: https://codereview.chromium.org/1397433002

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