[k8s] Run the tests using bluval

- Install pip requirements needed for bluval
- Run the k8s tests using bluval instead of directly using robot,
  thus allowing for more complex decisions regarding which tests to run
- Use relative paths in bluval
- Moved the input variable file in the tests folder (all things related
  to tests shoudl be there)
- Standardized the location and name of the log files

JIRA: VAL-28

Signed-off-by: Cristina Pauna <cristina.pauna@enea.com>
Change-Id: Ifc388d0df8b237d29239b62469f3f117e26e30f0