Dynamically set the CIDR for the public network

* Ensures that the public network and floating ip
  addresses are valid for each setup. Ping and SSH
  tests via the floating ip should pass after using this.
* updates:
  * remove explicit calls to sudo in packstack aio playbook
  * find public net and mask from ansible facts
  * update task name
  * only set the network/cidr as fact

Change-Id: I6247e048676b913530ab8b0c0f33d527997be743