hack: pass DBUS_SESSION_BUS_ADDRESS to the integration test suite

The test suite is executed via "env -i" with an explicit allow-list of
environment variables, so DBUS_SESSION_BUS_ADDRESS (exported by
.integration-daemon-start in rootless-systemd mode) never reached the
test binaries, nor the daemons they spawn via internal/testutil/daemon
("sudo --preserve-env"). Without it, runc inside those daemons cannot
detect the systemd user manager ("busctl --user" fails with the
per-daemon XDG_RUNTIME_DIR), assumes a rootful systemd, and fails to
create the container scope on the system bus:

    unable to start unit "docker-<id>.scope" ...: Permission denied

Also skip TestRunWithAlternativeContainerdShim in rootless-systemd
mode: the daemon only passes the SystemdCgroup option to the stock
runc runtime, so with an ad-hoc shim name runc falls back to the
cgroupfs driver and treats the systemd-style cgroupsPath as a literal
path, which cannot be created by a rootless daemon.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

hack/make/.integration-test-helpers

@@ -195,6 +195,7 @@ test_env() {
 		HOME="$ABS_DEST/fake-HOME" go telemetry off
 
 		env -i \
+			DBUS_SESSION_BUS_ADDRESS="$DBUS_SESSION_BUS_ADDRESS" \
 			DEST="$ABS_DEST" \
 			DOCKER_API_VERSION="$DOCKER_API_VERSION" \
 			DOCKER_BUILDKIT="$DOCKER_BUILDKIT" \

integration/container/run_linux_test.go

@@ -207,6 +207,11 @@ func TestRunConsoleSize(t *testing.T) {
 func TestRunWithAlternativeContainerdShim(t *testing.T) {
 	skip.If(t, testEnv.IsRemoteDaemon)
 	skip.If(t, testEnv.DaemonInfo.OSType != "linux")
+	// The daemon only passes the SystemdCgroup option to the stock runc
+	// runtime; with an ad-hoc shim name, runc falls back to the cgroupfs
+	// driver and treats the systemd-style cgroupsPath ("user.slice:docker:ID")
+	// as a literal path, which cannot be created by a rootless daemon.
+	skip.If(t, testEnv.IsRootless() && testEnv.DaemonInfo.CgroupDriver == "systemd", "alternative shims do not support the systemd cgroup driver in rootless mode")
 
 	ctx := testutil.StartSpan(baseContext, t)