Now the right way to register services with the Syncer is to call
`SetServices(groupName, []*services)`. This was required to allow
the Syncer to sync either the Client, Server, or Both using a
single Syncer.
This call is obsolete by a future commit that changes the canonical
source of truth to be consul.AgentServiceRegistration structs, which
means it is not necessary to construct AgentServiceRegistration
objects every time a registration is made, we just reuse the existing
object.
This has been done to allow the Server and Client to reuse the same
Syncer because the Agent may be running Client, Server, or both
simultaneously and we only want one Syncer object alive in the agent.
