Pass variables to robot testcases

Pass variables to robot testcases

* robot can take variables files in .yaml and .py formats
.yaml is more readable where .py can generate dynamic parametrs.
Here providing the both options.
* blueval engine updated to pass variables file.
* Decided to use simple (yaml) option and enhances it when needed

* We can make a standard, robot testcases can have variables but
comment them before committing. Looking at that users can update
variables file.

Signed-off-by: Naga Sugguna <ns156u@att.com>
Change-Id: I1df6efff22e86a7feaca5c2e641b7c130bb79138