Unset bootstrap-ansible variables between upgrades
Unset bootstrap-ansible variables between upgrades

During upgrade testing, unset environment variables used by the
bootstrap-ansible script to allow newer versions of Ansible and
global requirements to be installed.

Change-Id: I9a05325c6dca69674e026039beee6d914f0c0e41

yanyao/openstack-ansible,cloudnull/os-ansible-deployment,robb-romans/openstack-ansible,BjoernT/os-ansible-deployment,stackforge/os-ansible-deployment,bunchc/openstack-ansible,robb-romans/openstack-ansible,openstack/openstack-ansible,cfarquhar/openstack-ansible,bunchc/openstack-ansible,cloudnull/os-ansible-deployment,stackforge/os-ansible-deployment,BjoernT/os-ansible-deployment,BjoernT/openstack-ansible,BjoernT/openstack-ansible,BjoernT/os-ansible-deployment,cfarquhar/openstack-ansible,yanyao/openstack-ansible,openstack/openstack-ansible