submit_try: Obtain the list of trybots from the checked-in slaves.cfg

This should drastically speed up the script.

BUG=
R=epoger@google.com, rmistry@google.com

Author: borenet@google.com

Review URL: https://codereview.chromium.org/136683006

git-svn-id: http://skia.googlecode.com/svn/trunk@13071 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed