volumes: reload sftp on update

when diskPath changes, docker is busy holding on to the previous mount!
I guess this is because this is all somehow inode based.

src/volumes.js

@@ -122,6 +122,9 @@ async function update(volume, mountType, mountOptions) {
 
     const result = await database.query('UPDATE volumes SET mountOptionsJson=? WHERE id=?', [ JSON.stringify(mountOptions), volume.id ]);
     if (result.affectedRows !== 1) throw new BoxError(BoxError.NOT_FOUND, 'Volume not found');
+
+    // when diskPath or remoteDir is changed, we have to "rebind" the docker volumes
+    services.rebuildService('sftp', NOOP_CALLBACK);
 }
 
 async function getStatus(volume) {