Skip CRIU tests when $RUNC_USE_SYSTEMD for now

These tests sometimes hang, so let's skip them for now.

Tested:
  $ sudo make localintegration TESTPATH='/checkpoint.bats' RUNC_USE_SYSTEMD=1

The 5 tests in this test suite will be skipped.

Signed-off-by: Filipe Brandenburger <filbranden@google.com>

tests/integration/checkpoint.bats

@@ -3,6 +3,10 @@
 load helpers
 
 function setup() {
+  if [[ -n "${RUNC_USE_SYSTEMD}" ]] ; then
+    skip "CRIU test suite is skipped on systemd cgroup driver for now."
+  fi
+
   teardown_busybox
   setup_busybox
 }