Make DevicesGroup's "TestingSkipFinalCheck" attribute public

Users would like to have the possibility to skip checks for their
tests the same way they are skipped within the tests in runc.

Not exposing this variable makes it very hard to test components
that use this library. To avoid copying-and-pasting the code
into outside projects this variable sould be exposed to the users.

Signed-off-by: Itamar Holder <iholder@redhat.com>

libcontainer/cgroups/fs/devices.go

@@ -13,7 +13,7 @@ import (
 )
 
 type DevicesGroup struct {
-	testingSkipFinalCheck bool
+	TestingSkipFinalCheck bool
 }
 
 func (s *DevicesGroup) Name() string {
@@ -90,7 +90,7 @@ func (s *DevicesGroup) Set(path string, r *configs.Resources) error {
 	//
 	// This safety-check is skipped for the unit tests because we cannot
 	// currently mock devices.list correctly.
-	if !s.testingSkipFinalCheck {
+	if !s.TestingSkipFinalCheck {
 		currentAfter, err := loadEmulator(path)
 		if err != nil {
 			return err

libcontainer/cgroups/fs/devices_test.go

@@ -29,7 +29,7 @@ func TestDevicesSetAllow(t *testing.T) {
 		},
 	}
 
-	d := &DevicesGroup{testingSkipFinalCheck: true}
+	d := &DevicesGroup{TestingSkipFinalCheck: true}
 	if err := d.Set(path, r); err != nil {
 		t.Fatal(err)
 	}