Clean up run-blink-httpd, run-blink-websocketserver, add tests.

Last in the series of refactoring patches to clean up all the layout test
server code and helpers.

R=scottmg@chromium.org
BUG=30536

Review URL: https://codereview.chromium.org/135653016

git-svn-id: svn://svn.chromium.org/blink/trunk@167562 bbb929c8-8fbe-4397-9dbb-9b2b20218538