System test additions

- run --userns=keep-id: confirm that $HOME gets set (#8013)

 - inspect: confirm that JSON output is a sane number of
   lines (10 or more), not an unreadable one-liner (#8011
   and #8021). Do so with image, pod, network, volume
   because the code paths might be different.

 - cgroups: confirm that 'run' preserves cgroup manager (#7970)

 - sdnotify: reenable tests, and hope CI doesn't hang. This
   test was disabled on August 18 because CI jobs were hanging
   and timing out. My suspicion was that it was #7316, which
   in turn seems to have hinged on conmon #182. The latter
   was merged on Sep 16, so let's cross our fingers and see
   what happens.

Also: remove inaccurate warning from a networking test.

And, wow, fix is_cgroupsv2(), it has never actually worked.

Signed-off-by: Ed Santiago <santiago@redhat.com>

test/system/160-volumes.bats

@@ -213,6 +213,12 @@ EOF
         run_podman volume create $vol
     done
 
+    # (Assert that output is formatted, not a one-line blob: #8011)
+    run_podman volume inspect ${v[1]}
+    if [[ "${#lines[*]}" -lt 10 ]]; then
+        die "Output from 'volume inspect' is only ${#lines[*]} lines; see #8011"
+    fi
+
     # Run two containers: one mounting v1, one mounting v2 & v3
     run_podman run --name c1 --volume ${v[1]}:/vol1 $IMAGE date
     run_podman run --name c2 --volume ${v[2]}:/vol2 -v ${v[3]}:/vol3 \