extra/vm: Cleanup: `expect` isn't required for `stbt power`

But it is required for the selftests.
extra/vm: Remove workaround for stbt-tv pre-0.15
debian & fedora packages: Install lsof

Used by `stbt batch run` since stb-tester 0.15 to provide additional
information when a Blackmagic video-capture card appears to have frozen.

This may well be installed already as a dependency of another package,
but it doesn't hurt to list it explicitly.
extra/vm: Update to Ubuntu 14.04 for GStreamer 1 support

Ubuntu 12.04 doesn't have GStreamer 1 packages, so this didn't work at
all since a071a9cc (Port to GStreamer 1.0). Now that Ubuntu 14.04
LTS (Long-Term Support) is out, let's use it.

Vagrant themselves don't provide an Ubuntu 14.04 image, so I'm using one
provided by Ubuntu. There doesn't seem to be a stable link to builds
more than a few days old, so I'm using the current (nightly) build,
which should hopefully be ok now that 14.04 is released & officially
stable. An alternative would be to use the images by
phusionpassenger.com (a web-server / application-server outfit) but they
don't have a 32-bit image and I didn't want to change too many variables
at once. See the list of available images at http://www.vagrantbox.es/

Also install the right version of stb-tester and gstreamer-completion
for GStreamer 1.
extra/vm: Install stb-tester from PPA

Instead of building it from source. This results in a more standardised
configuration, rather than whatever version of the stb-tester source
code the user happened to have checked out. It also gives us one more
way of testing the binary package for Ubuntu.

We still mount the stb-tester source folder in case the user is an
stb-tester developer who wants to run the selftests, install a
development version, etc.  For the same reason we still install
stb-tester's dev dependencies in setup.sh; we don't need to list
the run-time dependencies because they will be installed by
`apt-get install stb-tester`.
Merge pull request #158 from drothlis/vm-1404lts

Update VM scripts in `extra/vm/` to Ubuntu 14.04