Teach webkit-patch update-flaky-tests how to upload a change

I accidentally already landed part of this support
in an earlier change, but this makes --upload actually
work.  You can see an example change here:
https://codereview.chromium.org/308743011/
(which again accidentally includes this change).

This also adds a hack-and-slash version of sheriff-calendar
code which I and Eric Boren originally wrote for the AutoRollBot
but that lives in a different repository:
https://chromium.googlesource.com/chromium/tools/build/+/master/scripts/tools/blink_roller/auto_roll.py

This combined with a cron job should make
it easy for gardeners to keep FlakyTests up to date.

Looking at 308743011, we clearly need to address some
of this marauding flakiness as FlakyTests should be
a very stable file.  Right now it is changing by the hour.

BUG=242366

Review URL: https://codereview.chromium.org/307183002

git-svn-id: svn://svn.chromium.org/blink/trunk@175228 bbb929c8-8fbe-4397-9dbb-9b2b20218538