gstreamer1.0: disable flaky baseparser tests

There are three baseparser tests which are causing trouble on the AB,
so disable them as we've filed an upstream bug.

Also fix a typo when we were attempting to disable parser_pull_short_read
where a colon was used instead of a comma.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>