WKR (new-commit-bot) is too slow

WKR (new-commit-bot) is too slow
https://bugs.webkit.org/show_bug.cgi?id=110087

Reviewed by Geoffrey Garen.

Running "svn up" or "git svn fetch" is way too slow (takes 2-3 minutes) on the machine I'm running the bot.
Just run "svn log -r <revision>" instead to cut down the delay.

Unfortunately, this work around doesn't work in a git checkout but who cares given I'm the one running the bot.

* Scripts/webkitpy/tool/commands/newcommitbot.py:
(NewCommitBot):
(NewCommitBot.next_work_item):
(NewCommitBot._is_empty_log):
(NewCommitBot._update_checkout):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@147984 268f45cc-cd09-0410-ab3c-d52691b4dbfc