Merge pull request #500 from hqhq/hq_add_set_for_systemd

add Set support for systemd based cgroup

cgroups/systemd/apply_systemd.go

@@ -382,7 +382,17 @@ func (m *Manager) GetStats() (*cgroups.Stats, error) {
 }
 
 func (m *Manager) Set(container *configs.Config) error {
-	panic("not implemented")
+	for name, path := range m.Paths {
+		sys, ok := subsystems[name]
+		if !ok || !cgroups.PathExists(path) {
+			continue
+		}
+		if err := sys.Set(path, container.Cgroups); err != nil {
+			return err
+		}
+	}
+
+	return nil
 }
 
 func getUnitName(c *configs.Cgroup) string {