Ensure proxy check is short circuit
Ensure proxy check is short circuit

Otherwise when repo_pkg_cache_enabled is false and repo_pkg_cache_url
is https, proxy_check.status will cause an attribute error.

Change-Id: Ib0f5326865d11ecbb718e586441c4f7c2a754c9d

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