Allow lab status to block based on a build regex.

Previously, the lab status could contain a string to block testing
based on the board.  With this change, the status can block any
build that matches a regex in the status.  This allows closing the
lab to either a build or a milestone.  It also allows closing the
lab for other more specific conditions, for anyone desperate enough
to want to.

BUG=chromium:220934
TEST=unit tests

Change-Id: I8a44f5e9be504415a7c5bd73c714c778bf684d2c
Reviewed-on: https://chromium-review.googlesource.com/179544
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Alex Miller <milleral@chromium.org>
Commit-Queue: Richard Barnette <jrbarnette@chromium.org>
7 files changed