Inventory generation should not happen unless inventory layout is supplied

[herlo]

While running linch-pin and NOT requesting a inventory, because no inventory_layout_file was provided (as below).

ansible-playbook -vvv ~/Projects/centos/git/linch-pin/provision/site.yml -e "state=present topology='~/Projects/centos/git/paas-ci/config/topologies/openstack-3node-cluster.yml'"

..snip...

TASK [inventory_gen : Generate inventories] ************************************
task path: /home/herlo/Projects/centos/git/linch-pin/provision/roles/inventory_gen/tasks/main.yml:47
failed: [localhost] (item=[u'aws', u'/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory']) => {"failed": true, "invocation": {"module_args": {"dest": "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory.aws", "src": "templates/aws_inventory_formatter.j2"}, "module_name": "template"}, "item": ["aws", "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory"], "msg": "IndexError: pop from empty list"}
failed: [localhost] (item=[u'gcloud', u'/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory']) => {"failed": true, "invocation": {"module_args": {"dest": "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory.gcloud", "src": "templates/gcloud_inventory_formatter.j2"}, "module_name": "template"}, "item": ["gcloud", "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory"], "msg": "IndexError: pop from empty list"}
failed: [localhost] (item=[u'openstack', u'/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory']) => {"failed": true, "invocation": {"module_args": {"dest": "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory.openstack", "src": "templates/openstack_inventory_formatter.j2"}, "module_name": "template"}, "item": ["openstack", "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory"], "msg": "IndexError: pop from empty list"}
failed: [localhost] (item=[u'generic', u'/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory']) => {"failed": true, "invocation": {"module_args": {"dest": "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory.generic", "src": "templates/generic_inventory_formatter.j2"}, "module_name": "template"}, "item": ["generic", "/home/herlo/Projects/centos/git/linch-pin/inventory_outputs/openstack_topology.inventory"], "msg": "IndexError: pop from empty list"}

NO MORE HOSTS LEFT *************************************************************
    to retry, use: --limit @/home/herlo/Projects/centos/git/linch-pin/provision/site.retry

PLAY RECAP *********************************************************************
localhost                  : ok=48   changed=3    unreachable=0    failed=1