libct: Signal: honor RootlessCgroups

`signalAllProcesses()` depends on the cgroup and is expected to fail
when runc is running in rootless without an access to the cgroup.

When `RootlessCgroups` is set to `true`, runc just ignores the error
from `signalAllProcesses` and may leak some processes running.
(See the comments in PR 4395)
In the future, runc should walk the process tree to avoid such a leak.

Note that `RootlessCgroups` is a misnomer; it is set to `false` despite
the name when cgroup v2 delegation is configured.
This is expected to be renamed in a separate commit.

Fix issue 4394

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

tests/integration/kill.bats

@@ -133,3 +133,27 @@ test_host_pidns_kill() {
 	test_host_pidns_kill
 	unset KILL_INIT
 }
+
+# https://github.com/opencontainers/runc/issues/4394 (cgroup v1, rootless)
+@test "kill KILL [shared pidns]" {
+	update_config '.process.args = ["sleep", "infinity"]'
+
+	runc run -d --console-socket "$CONSOLE_SOCKET" target_ctr
+	[ "$status" -eq 0 ]
+	testcontainer target_ctr running
+	target_pid="$(__runc state target_ctr | jq .pid)"
+	update_config '.linux.namespaces |= map(if .type == "user" or .type == "pid" then (.path = "/proc/'"$target_pid"'/ns/" + .type) else . end) | del(.linux.uidMappings) | del(.linux.gidMappings)'
+
+	runc run -d --console-socket "$CONSOLE_SOCKET" attached_ctr
+	[ "$status" -eq 0 ]
+	testcontainer attached_ctr running
+
+	runc kill attached_ctr 9
+	[ "$status" -eq 0 ]
+
+	runc delete --force attached_ctr
+	[ "$status" -eq 0 ]
+
+	runc delete --force target_ctr
+	[ "$status" -eq 0 ]
+}