[presubmit] Allow referencing non-Chromium Rietveld bugs in BUG= line
[presubmit] Allow referencing non-Chromium Rietveld bugs in BUG= line

This patch modifies the global Catapult presubmit script to:

  1. allow non-Chromium Rietveld bug references (namely 'v8:NNNNNN') in patch
     description BUG= lines,
  2. enforce that Rietveld bugs are listed before Catapult bugs so that
     Rietveld would convert them to hyperlinks and
  3. display a (non-error) message if there is no BUG= line suggesting the
     author adds one.

Note that the non-Chromium Rietveld repository names must still be manually
whitelisted. This is to prevent people from submitting patches with misspelled
bugs (e.g. 'ctpult:666').

Review-Url: https://codereview.chromium.org/2029533002

sahiljain/catapult,catapult-project/catapult-csm,sahiljain/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,sahiljain/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,sahiljain/catapult,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult,sahiljain/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult-csm,sahiljain/catapult,catapult-project/catapult