tests/int/events: skip oom test if no swap

In case swap cgroup control is not available, the "event oom" test gives
the following error:

> # not ok 30 events oom
> # (in test file tests/integration/events.bats, line 134)
> #   `[ "$status" -eq 0 ]' failed
> # <....>
> # runc run -d --console-socket /tmp/console.sock test_busybox (status=1):
> # time="2020-05-29T02:10:20Z" level=warning msg="signal: killed"
> # time="2020-05-29T02:10:20Z" level=error msg="container_linux.go:353: starting container process caused: process_linux.go:437: container init caused: process_linux.go:403: setting cgroup config for procHooks process caused: failed to write \"33554432\" to \"/sys/fs/cgroup/memory/test_busybox/memory.memsw.limit_in_bytes\": open /sys/fs/cgroup/memory/test_busybox/memory.memsw.limit_in_bytes: permission denied"

When I try to run the test without setting the swap limit, the shell
process is still getting killed, but the test hangs. I am not sure what
the reason is, but realistically this test is hard to perform without
the swap limit, so let's require cgroup swap for it.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

tests/integration/events.bats

@@ -112,11 +112,11 @@ function teardown() {
   [ "$status" -eq 0 ]
 }
 
-@test "events oom " {
+@test "events oom" {
   # XXX: currently cgroups require root containers.
-  requires root
+  requires root cgroups_swap
   init_cgroup_paths
-  
+
   # we need the container to hit OOM, so disable swap
   # ("swap" here is actually memory+swap)
   DATA=$(cat <<EOF

tests/integration/helpers.bash

@@ -257,6 +257,12 @@ function requires() {
 				skip_me=1
 			fi
 			;;
+		cgroups_swap)
+			init_cgroup_paths
+			if [ $CGROUP_UNIFIED = "no" -a ! -e "${CGROUP_MEMORY_BASE_PATH}/memory.memsw.limit_in_bytes" ]; then
+				skip_me=1
+			fi
+			;;
 		cgroups_v1)
 			init_cgroup_paths
 			if [ "$CGROUP_UNIFIED" != "no" ]; then