test_that_video_index_is_written_on_eos is robust under load

When running tests in parallel, this test would occasionally fail with:

    File "webminspector/webminspector.py", line 116, in <module>
      main()
    File "webminspector/webminspector.py", line 97, in main
      pos = segment.SearchLevelOneElements(file_, pos)
    File "webminspector/webm.py", line 560, in SearchLevelOneElements
      size, start_pos = ReadOneByteForElementIdSize(file_, pos)
    File "webminspector/webm.py", line 53, in ReadOneByteForElementIdSize
      file_.seek(pos)
    TypeError: 'NoneType' object cannot be interpreted as an index

Presumably `stbt run` didn't manage to send sufficient data for the
video to be written properly.

This commit re-runs the test with a longer `sleep` if it fails the first
time. I didn't simply increase the timeout because this test doesn't
usually fail when running the tests sequentially (if you don't have GNU
`parallel` installed), so I didn't want to increase the run-time of
a sequential `make check` unnecessarily.
rpm spec file: Add missing dependency "python-flask"

Used by `stbt batch instaweb`.

Note that python-jinja2 is implicitly installed by python-flask, but
I've kept python-jinja2 as an explicit dependency of stb-tester because
stbt.py uses jinja2 outside of flask (to generate the debug html files
from `stbt run -vv`).
Add scripts for creating Ubuntu PPA with our dependencies

When we migrated to GStreamer 1.0 we had to patch some regressions
which had made their way into GStreamer since 0.10.  These patches
have been submitted upstream but not yet made their way into a
stable release of GStreamer, let alone the major distros.  This
makes it very difficult for our users to install and deploy
stb-tester.  This is an attempt at simplifying this process by
providing appropriately patched versions of our dependencies in an
Ubuntu PPA.

This also includes a dkms package to allow distributing a patched
version of the uvcvideo driver.  This is required for Smart TV
support with the Logitech C920 driver.

The code isn't beautiful but it lives in extra/ and is a tools
for maintainers rather than users or developers.
PPA Support: disable `make check` as a part of building Debian package

Disable `make check` for now as it gives us difficulty on Ubuntu's PPA
build farm.  Specifically the lack of a terminal prevents expect from
working and there are timing issues due to the load the build machines are
under.

This commit should be reverted once these issues have been investigated
and resolved but for now PPAs are more important.
PPA Support: Add make target `make ppa-publish`

This makes it easy to publish stb-tester packages for Ubuntu.