servicedispatcher: add option to wrap service manager

`servicedispatcher manager` runs a service on a port where
all calls are redirected to servicemanager.

This works around b/191059588, because we don't support running
RpcServer directly on servicemanager yet.

Test: pass
Bug: 190233850
Bug: 191059588

Change-Id: I69ef50ccf3ba73e3a2085211ecce99425818aedf