Have all the rebaseline commands only rebaseline failures that are actually happening on the bots.

At first, I thought this only made sense for auto-rebaseline, but I think it
never makes sense to try to do a rebaseline for a failure that isn't happening on
the bots.

This fixes the bug where rebaselining will always grab the flaky result
because it grabs whatever's in the accumulated results directory

Review URL: https://chromiumcodereview.appspot.com/22108002

git-svn-id: svn://svn.chromium.org/blink/trunk@155897 bbb929c8-8fbe-4397-9dbb-9b2b20218538