The changes in the realmd dbus interface are futureproofing to
support cancellation.
In addition during this time of interface flux, check the
daemon version number to make sure we can talk to it.
https://bugzilla.gnome.org/show_bug.cgi?id=678105
* Use realmd for domain joining and lookup, runtime dependency
* Validate join domain correctly
* Add UmRealmManager for handling some stuff above the autogenerated
realmd dbus code
* Show a dialog if the user's credentials cannot be used to join
the domain. Prompt for admin creds.
* Register the user's login with the AccountsService
* This depends on the CacheUser() method of AccountsService
https://bugzilla.gnome.org/show_bug.cgi?id=677548
