* Add passlib to RHEL test instance
This looks like the only tests instance that is missing this libary. It is needed for vars_prompt tests.
* Create setup roles for pexect and passlib
Switch to using aliases rather than installing directly in the test scripts
* Only template values in vars_prompt rather than all vars
This allows the use of variables in vars_prompt fields but allows variables entered in the prompt to affect play vars rather than throwing an undefined error.
Only post validate if there was a vars_prompt
* Add tests for vars_prompt