use ansible 1.7.2
as of now the latest release of ansible is 1.8.0. This has broken
Postgresql modules, so ansible cannot install ansible tower.
I'm specifying a known-good ansible so this deployment will continue to
work. We should bump this up or revert when ansible is fixed.
testing out the latest 1.8.1 fix for the postgres bug
Merge pull request #19 from rackspace-orchestration-templates/postgresfix

latest version of ansible fixes the postgres bug.