Copy canary.go task driver from skia repo to buildbot repo
Copy canary.go task driver from skia repo to buildbot repo

Next steps:
* Roll infra.git in skia repo and use canary.go from buildbot repo.
* Create a canary task driver CIPD bot (similar to
  validate_autoroll_configs).

More context is in the below issue.

Bug: skia:12657
Change-Id: I2dadf71b8490f4ebf188a15ece45dee7d0b838d0
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/472800
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

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