zuul: Switch to the Zuulv3 grenade job
zuul: Switch to the Zuulv3 grenade job

This change switches the single node legacy grenade-py3 job over to the
newly introduced Zuulv3 based grenade job.

Change-Id: I212692905a1d645cd911c2a161c13c794c0e0f4d

mahak/nova,mahak/nova,klmitch/nova,openstack/nova,mahak/nova,openstack/nova,klmitch/nova,openstack/nova,klmitch/nova,klmitch/nova