rsync: default to sync-rsync-verify-jobs = 1 (bug 650696)

Some users have reported that using all processors to verify
manifests results in overloading, therefore default to using
a single processor. On modern hardware, verification of the
gentoo repository completes in less than 20 seconds, so using
multiple processors is not really necessary. Also, gemato-13.0
disables parallel verification due to the unresolved deadlock
issue reported in bug 647964, so this brings the default
portage configuration into alignment with current gemato
behavior.

Bug: https://bugs.gentoo.org/650696
Bug: https://bugs.gentoo.org/647964
3 files changed