[autotest] Expand DevServer class to support control-file related calls

Add the ability to call the control_files/ endpoint on the dev server.

BUG=chromium-os:24985
TEST=dev_server_unittest.py

Change-Id: If20e7c6d1f13813cd10511c34d64e9ffddfb37f4
Reviewed-on: https://gerrit.chromium.org/gerrit/14302
Commit-Ready: Chris Masone <cmasone@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
Tested-by: Chris Masone <cmasone@chromium.org>
4 files changed