MasterRpcServices seems to access directly a bunch of members of HMaster. I think this is because when we split HMaster and MaterRpcServices we just did a find & replace.
I was trying to mock and have a different AssignmentManager and ServerManager but it got impossible with those access directly.
so, here a patch to avoid the direct access to AM and SM.
There are many more members that can be made private but I'm lazy. so this pass is only AM, SM related