cbuildbot: split out release engineering builder logic

Start a new release engineering builder module to hold the various RE
related builders.  This is not for our "release" configs (i.e. canaries)
but for general release engineering needs.

BUG=brillo:134, chromium:299943
TEST=`./cbuildbot/run_tests` passes

Change-Id: I80bfbcfc18e1a208edce3a4c5eb76dc9b31701f1
Reviewed-on: https://chromium-review.googlesource.com/253710
Trybot-Ready: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
6 files changed