Do not run ZFS tests when ZFS is unsupported in the environment.

The recent patch b4af4022 adds tests
to storagepoolxml2xmltest for the optional ZFS feature. When ZFS is
not included in the configuration these tests should not / cannot be
run. Modify the test source file to check for use of the feature and
compile in the tests accordingly.
Signed-off-by: NGary R Hook <gary.hook@nimboxx.com>