GitLab

Changes in this CL:
 - In request_build.py, add a URL for linux try bot.
 - Add sample config for functional bisect.
 - Make perf-related config parameters optional.
 - Use builder type when starting build try jobs, and when fetching builds.

A few other changes:
 - Update bisect_perf_regression.py file docstring.
 - Rename _BuilderTryjob to _StartBuilderTryJob and refactor.
 - Remove unused code in request_build.py.

Proposed follow-up:
 - Move functions related to builder to be methods of one class, so that the builder-specific info/logic (e.g. builder bot and archive location) is in one place.

BUG=

Review URL: https://codereview.chromium.org/806943007

Cr-Commit-Position: refs/heads/master@{#313415}