This consists of the following pieces:
1. Makes servers using the bouncer send realm_uuid in requests for token
registration. (Sidenote: realm_uuid is already sent in the "send
notification" codepath as of
48db4bf854)
2. This allows the bouncer to tie RemotePushDeviceToken to the
RemoteRealm with matching realm_uuid at registration time.
3. Introduce handling of some potential weird edge cases around the
realm_uuid and RemoteRealm objects in get_remote_realm_helper.
Mateusz Mandera