Install python2 in Ubuntu 16.04 or CentOS 7
Install python2 in Ubuntu 16.04 or CentOS 7

After Ubuntu 16.04 or CentOS 7 version, the
python2 is not installed by default. This
modification attempts to verify if python2
is installed or not in the target hosts and
install it if needed.

Change-Id: I2cbf2f144ce5bd4bc524ea0c49c3405814e27d69

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