e2e-tests: Test that sha & tests are updated after a git push

First true integration test. It requires a real "stb-tester ONE"
appliance, plus an HTTP reverse proxy that serves:

* The (local) web-ui code at http://localhost:8000/app/
* Everything else (http://localhost:8000/*) redirected to the stb-tester
  ONE. In particular:
    * the back-end stb-tester service at /api
    * the back-end git server at /git

This test covers the functionality tested by the existing tests, so I've
removed them.