cbuildbot_config: Mark release builds important.
This introduces a variable, "IS_RELEASE_BRANCH", that, when True, causes
all important canaries to be assigned to the release waterfall.
Consequently, manual release waterfall provisioning has been removed.
It also updates the configurations to remove the 'important' flag from
configs that don't belong on the release waterfall.
BUG=chromium:456203
TEST=`./cbuildbot/run_tests`
Change-Id: If6cb48e0e27d8b1f7486183a53c03ccaec86a28b
Reviewed-on: https://chromium-review.googlesource.com/266093
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Daniel Jacques <dnj@chromium.org>
Tested-by: Daniel Jacques <dnj@chromium.org>
2 files changed
