If reservation.error then let reservation raise its own error

This replaces a code path that didn't work (name & index didn't exist)
and uses the NetworkReservation#handle_error method correctly
as per how Network#reserve! similarly handles NetworkReservation
errors.

Passing human-readable text "resource-pool-updater" as the "origin"
since there is no "job_name/index" during the ResourcePoolUpdater
refill sequence.