Add locking to Sync() on containers

Previously not needed as it only worked inside of Batch(), but
now that it can be called anywhere we need to add mutual
exclusion on its config changes.

Signed-off-by: Matthew Heon <mheon@redhat.com>

libpod/container_api.go

@@ -685,6 +685,11 @@ func (c *Container) Batch(batchFunc func(*Container) error) error {
 // Running a manual Sync() ensures that container state will be correct in
 // such situations.
 func (c *Container) Sync() error {
+	if !c.batched {
+		c.lock.Lock()
+		defer c.lock.Unlock()
+	}
+
 	// If runtime knows about the container, update its status in runtime
 	// And then save back to disk
 	if (c.state.State != ContainerStateUnknown) &&