xfs/43[4-6]: make module reloading optional

xfs/43[4-6]: make module reloading optional

These three tests examine two things -- first, can xfs CoW staging
extent recovery handle corruptions in the refcount btree gracefully; and
second, can we avoid leaking incore inodes and dquots.

The only cheap way to check the second condition is to rmmod and
modprobe the XFS module, which triggers leak detection when rmmod tears
down the caches.  Currently, the entire test is _notrun if module
reloading doesn't work.

Unfortunately, these tests never run for the majority of XFS developers
because their testbeds either compile the xfs kernel driver into vmlinux
statically or the rootfs is xfs so the module cannot be reloaded.  The
author's testbed boots from NFS and does not have this limitation.

Because we've had repeated instances of CoW recovery regressions not
being caught by testing until for-next hits my machine, let's make the
module reloading optional in all three tests to improve coverage.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>