[autotest] Add a library wrapping around statsd for ease of use.

There's a few issues with statsd, such that having a nice wrapper around
it would be convenient:
 * Stats logged by a locally run testing setup and stats logged by prod
   would by default go into the same "bucket" on graphite.
 * Use of |sendto()| involves resolving STATSD_HOST, which would happen
   very frequently.
 * statsd logs a large amount of information, which one could just as
   easily see on chromeos-stats/
 * A connection would need to be setup in each place where one wants to
   send stats.

BUG=chromium-os:36682
TEST=Added a tick stat to the scheduler, it appears on chromeos-stats/
     under stats/timers/milleral/scheduler/tick

Change-Id: I4572ee6fde5e14ab2ba0dfb3d776268849519cd2
Reviewed-on: https://gerrit.chromium.org/gerrit/45138
Tested-by: Alex Miller <milleral@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
3 files changed