buildbot_utils: for release builds, get logs from the 'release' builder.

The individual ${BOARD}-release builders are now grouped together
into one 'release' builder.

BUG=None
TEST=None

Change-Id: Ie0a2ea1298c63f71385f4f9331e611d8ac22efca
Reviewed-on: https://chrome-internal-review.googlesource.com/225253
Reviewed-by: Caroline Tice <cmtice@google.com>
Commit-Queue: Rahul Chaudhry <rahulchaudhry@google.com>
Tested-by: Rahul Chaudhry <rahulchaudhry@google.com>
1 file changed