test-cgroup-util: Skip procs analysis without cgroupfs

cg_pidref_get_path() cannot work (current implementaion) without
cgroupfs (when it checks unified or not setup). Similarly,
cg_pidref_get_unit() assumes all processes are part of a unit. So carry
out the test only when running on a systemd setup.

src/test/test-cgroup-util.c

@@ -198,7 +198,7 @@ TEST(get_paths, .sd_booted = true) {
         log_info("Root = %s", a);
 }
 
-TEST(proc) {
+TEST(proc, .sd_booted = true) {
         _cleanup_closedir_ DIR *d = NULL;
         int r;