cephfs: add a test case for calling Statx on an invalid mount
cephfs: add a test case for calling Statx on an invalid mount

Adding this test case gets test coverage to 100% for path.go.

Signed-off-by: John Mulligan <eda8ad33169deab44f9fe65847f99e368da6c91b@redhat.com>

ceph/go-ceph,ceph/go-ceph,ceph/go-ceph