topology_output_file requires .yaml due to update to jinja2 2.8

[herlo]

Because we updated to jinja2 2.8, ansible expects .yaml, .yml, or .json extensions for files that are being processed internally. Thus, calling linch-pin without topology_output_file=somevalue.yaml will result in a file that ends in .output.

Here's an example of the error from jenkins: https://ci.centos.org/job/paas-bfs-origin-0-test-matrix/PYTHON=system-CPython-2.7,TOPOLOGY=duffy_3node_cluster,nodes=paas-sig-ci-slave01/1/console

16:01:44 fatal: [localhost]: FAILED! => {"ansible_facts": {}, "changed": false, "failed": true, "message": "/home/sig-paas/workspace/paas-bfs-origin-0-test-matrix/PYTHON/system-CPython-2.7/TOPOLOGY/duffy_3node_cluster/nodes/paas-sig-ci-slave01/linch-pin/outputs/duffy_3node_cluster.output does not have a valid extension: yaml, yml, json"}

[herlo]

#104 provided the complete fix. Thanks @arilivigni