container: Avoid reinstalling tests in pts

pts will automatically detect when the system changes (CPU, compiler,
etc) and force a reinstall of the test in that case as an opportunity to
tune for the platform. But we don't want this behaviour when testing the
kernel; we want the user space to be constant. Additionally we don't
want to waste the extra time doing unneccessary recompiles. So let's
patch pts to avoid the forced reinstall. See the patch in the commit for
details.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>