MB-8109 Set pending transition for outdated updater groups

This was missing in MB-7522, commit ac82c60302422747e8804d566211a20684ec78fb.

Change-Id: I7a17b90b0aa4500956661fcd468e4978fbae0623
Reviewed-on: http://review.couchbase.org/25725
Reviewed-by: Fulu Li <fulu@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>