servicemanager: Overwrite old service when a new one is registered

We want to overwrite an old service with the same name as a new service
that is being added. The old one will be cleaned up as servicemanager
loses the reference to it.

Test: atest servicemanager_test && additional tests outlined in Bug
Bug: 162553096
Change-Id: I8835d9f7505367d83a0f29f1d928a07b3d57e56a