Merge pull request #102 from dhylands/dhylands-884273-default-channel

Bug 884273 - Remove default update channel, and let it default to what configure wants. r=kairo sr=ted
(cherry picked from commit d4e6ca10162b4d3d79052b5b4721c4495640493e)
Merge remote-tracking branch 'upstream/v1-train' into v1-train