CI: skip kernel-oplocks tests on older kernels

CI: skip kernel-oplocks tests on older kernels

The kernel of the gitlab shared runners container host has a bug in the
interaction between kernel oplocks and O_PATH opens which was fixed by
387e3746d01c34457d6a73688acd90428725070b in 5.3.1:

<https://kernel.googlesource.com/pub/scm/linux/kernel/git/jlayton/linux/+/refs/tags/locks-v5.3-1%5E%21/>

Don't actually start the OPLOCK5 test is kernel oplocks are not available,
instead of relying on the #ifdef HAVE_KERNEL_OPLOCKS_LINUX magic in torture.c.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>