Adds a property that triggers the file playback tests on
GstQaFileCheker. Also enable it in the gst-transcoding post file checks.
The implementation is simple, just create a playbin2 and use fakesinks
as sinks, set it to playing and wait for either EOS or ERROR messages.
Use our own custom comparison to allow to add more fine grained error
reporting. Also the encoding profile is_equal function is too strict as
it also compares profiles names, that doesn't matter to us.
This commit implementation is still initial and needs improvements as it
isn't using the restriction caps, which includes information that might not be
on the profile format caps.
It is an object that is capable to run a few file checks. The
implemented tests are: file size, duration, if the file is seekable and
comparing the file stream types with a encoding profile
