rebaseline_server: add actual_repo and actual_revision command line options

rebaseline_server: add actual_repo and actual_revision command line options

So, if you want to see divergences from expectations as of https://code.google.com/p/skia-autogen/source/detail?r=29365 , specify --actuals-revision 29365

This is also handy for testing rebaseline_server performance improvements against a static set of results.

BUG=skia:2248
NOTREECHECKS=True
NOTRY=True
R=borenet@google.com, bsalomon@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/193023002

git-svn-id: http://skia.googlecode.com/svn/trunk@13726 2bbb7eff-a529-9590-31e7-b0007b416f81