libct/cg: skip TestWriteCgroupFileHandlesInterrupt on CentOS 7

It's flaky (kernel bug?) and there's probably nothing we can do about
it.

Fixes #3418.

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

libcontainer/cgroups/file_test.go

@@ -8,9 +8,13 @@ import (
 	"strconv"
 	"testing"
 	"time"
+
+	"github.com/opencontainers/runc/internal/testutil"
 )
 
 func TestWriteCgroupFileHandlesInterrupt(t *testing.T) {
+	testutil.SkipOnCentOS(t, "Flaky (see #4318)", 7)
+
 	const (
 		memoryCgroupMount = "/sys/fs/cgroup/memory"
 		memoryLimit       = "memory.limit_in_bytes"