This was a vestige from when we used to need the unittest2 library for pre-2.7
compatibility. Now that we require Python 2.7, we aren't using that library
and this indirection wasn't doing any good.
This reverts commit 9c41c39913.
That commit used byte strings for the `if __name__ == '__main__'` pattern,
which was necessary when we were doing unicode_literals. But it is wrong on
Python 3, and now that we're liberated from unicode_literals, we need to go
back to native strings for this comparison.
* Add a check to ReplayGainGstCliTest that ensures that the required
initial gstreamer plugins can be loaded, skipping the test if it is not
the case instead of running it.
* Add a check to ReplayGainGstCliTest.test_cli_saves_track_gain for
checking if item.rg_track_peak and item.rg_track_gain is not None. If
they are None, it is assumed that the decoder plugins could not be
found, and the tests is skipped, as discussed on #1830.
Include import of __future__ features division, absolute_imports and
print_function everywhere. Don't add unicode_literals yet for it is
harder to convert.
Goal is smoothing the transition to python 3.
The first fix avoids contaminating all future tests if the plugin fails to
load. The second skips the CLI backend tests when the appropriate tool is not
available (just as we do with the GStreamer tests).
