Fix python prereq install task
Fix python prereq install task

It's not possible to check ansible_pkg_mgr yet because we haven't
gathered facts. This patch adjusts the task to run on all distros
but it only has an effect on Ubuntu systems without python installed.

Change-Id: I8859b740a4d190fb1548af7ed7df92c248e2c5a3

bunchc/openstack-ansible,cfarquhar/openstack-ansible,yanyao/openstack-ansible,bunchc/openstack-ansible,stackforge/os-ansible-deployment,openstack/openstack-ansible,cfarquhar/openstack-ansible,openstack/openstack-ansible,stackforge/os-ansible-deployment,yanyao/openstack-ansible