It is a random number, but it will in most cases give people a hint
that gst-validate reported a critical issue, and thus set the return
code, only by looking at it
Also make use of gst_validate_runner_print() in
gst-validate-transcoding.c as we were copy pasting that method there.
For instance, "fakesrc" will return a fakesrc, not a pipeline.
This is similar to what gst-launch does, and avoids calling
pipeline API on a non pipeline object (and thus asserting).
Makes the result a bit more readable than a compact multi-line list.
FIXME: Figure out how to print the description of the issues (which can
spawn multiple lines) in a nice way.
