[INTERNAL] UserListExtension class now uses the correct provider

As the network extensions are already incompatible with former
Saros version it is a good time for this change now.

Change-Id: Ida736c154ce3efa5013a966c6b6f08c8c8e11462
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/921
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>