Properly detect whether we're running on a buildbot.
Properly detect whether we're running on a buildbot.

BUILDBOT_BUILDERNAME is only set for bots using annotated steps, which
isn't all of them. This detects whether the username is "chrome-bot"
instead.

This check is currently only being used to decide whether to use
unittest's compact VM config or the default config.

R=rnystrom@google.com, sigmund@google.com

Review URL: https://codereview.chromium.org//58933006

git-svn-id: b889c0189f1adfea19efba192a3d7a5b889e4120@30206 260f80e4-7a28-3924-810f-c04153c831b5

Pacane/test,greglittlefield-wf/test,d2m/test,d2m/test,iglherme/Guttiest,apwilson/test,iglherme/Guttiest,greglittlefield-wf/test,apwilson/test,grouma/test,kevmoo/test,iglherme/Guttiest,kevmoo/test,d2m/test,apwilson/test,grouma/test,greglittlefield-wf/test,Pacane/test,kevmoo/test,grouma/test