last-green-revision should report the revision that succeeded on all bots

last-green-revision should report the revision that succeeded on all bots
https://bugs.webkit.org/show_bug.cgi?id=76109

Reviewed by Adam Barth.

Add an algorithm to find the last known good revision among the specified bots. For a revision to be
considered green by this algorithm, all matching builders must have a successful run at the revision
or two consecutive successful runs before and after the revision.

Also fixed a bug in irc_command that the result wasn't posted on IRC properly and a bug in queries.py
that resulted in an exception when the user didn't pass BUILDER_NAME argument.

* Scripts/webkitpy/common/net/buildbot/buildbot.py:
(BuildBot._revisions_for_builder):
(BuildBot):
(BuildBot._find_green_revision):
(BuildBot.last_green_revision):
* Scripts/webkitpy/common/net/buildbot/buildbot_mock.py:
(MockBuildBot.last_green_revision):
* Scripts/webkitpy/common/net/buildbot/buildbot_unittest.py:
(test_revisions_for_builder):
(test_find_green_revision):
(test_last_green_revision):
* Scripts/webkitpy/tool/bot/irc_command.py:
(LastGreenRevision.execute):
* Scripts/webkitpy/tool/bot/sheriffircbot_unittest.py:
(SheriffIRCBotTest.test_lgr):
* Scripts/webkitpy/tool/commands/queries.py:
(LastGreenRevision):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@104754 268f45cc-cd09-0410-ab3c-d52691b4dbfc