contint: invoke gerrit-sync-ve-push.sh as jenkins

gerrit-sync-ve-push.sh needs to be run as 'jenkins' user to be able to
use the SSH credentials of Gerrit 'jenkins-bot' user.  That is used by
the script to push an update of mediawiki/extensions.git to workaround
VisualEditor no more updating in Gerrit.

I have made the sudo_user at the host level since that is where all of
them are made already.

Bug: 49846
Change-Id: Ib0c260667803e75586eca5e19a6466496c0f7510