functional: use vexxhost-specific nodes with nested virt
functional: use vexxhost-specific nodes with nested virt

This patch changes the intergration jobs to use nodes which are
at VEXXHOST that come with supported nested virtualization in
order to allow for the functional jobs to finish on-time.

Change-Id: Ie275caac1a40fb3f10a0653b66611d2ba9d1c470
Story: #2002589
Task: #28341

openstack/magnum,openstack/magnum,ArchiFleKs/magnum,ArchiFleKs/magnum