LazyServiceRegistrar: Add flag to prevent shutdown

This flag can be used to temporarily prevent dynamic services from being killed. For example, if a service needs to perform a task in the background it can set this flag and then disable it once the task is complete. The service will then go back to standard lazy behavior.

Bug: 150967269
Test: aidl_lazy_test
Change-Id: I840bbe4b6b0406f0e4de610367290448e7edd3de