integration: fix mis-use of libcontainer.Factory

For some reason, libcontainer/integration has a whole bunch of incorrect
usages of libcontainer.Factory -- causing test failures with a set of
security patches that will be published soon. Fixing ths is fairly
trivial (switch to creating a new libcontainer.Factory once in each
process, rather than creating one in TestMain globally).

Signed-off-by: Aleksa Sarai <asarai@suse.de>

libcontainer/integration/utils_test.go

@@ -77,6 +77,7 @@ func newTestRoot() (string, error) {
 	if err := os.MkdirAll(dir, 0700); err != nil {
 		return "", err
 	}
+	testRoots = append(testRoots, dir)
 	return dir, nil
 }
 
@@ -127,9 +128,20 @@ func newContainer(config *configs.Config) (libcontainer.Container, error) {
 }
 
 func newContainerWithName(name string, config *configs.Config) (libcontainer.Container, error) {
-	f := factory
+	root, err := newTestRoot()
+	if err != nil {
+		return nil, err
+	}
+
+	f, err := libcontainer.New(root, libcontainer.Cgroupfs)
+	if err != nil {
+		return nil, err
+	}
 	if config.Cgroups != nil && config.Cgroups.Parent == "system.slice" {
-		f = systemdFactory
+		f, err = libcontainer.New(root, libcontainer.SystemdCgroups)
+		if err != nil {
+			return nil, err
+		}
 	}
 	return f.Create(name, config)
 }