Add a health check tool for use by the deployment tools.
Add a health check tool for use by the deployment tools.

Bug: 812965
Change-Id: I3edcc8830f186c6b02e3d2071a8d7c73b54a4193
Reviewed-on: https://chromium-review.googlesource.com/940382
Reviewed-by: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>
Commit-Queue: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py