Organize file structure for tests

Reorganized the tests following these rules
- all tests have been put under *tests* folder
- all tests are organised under folders named
  by their correspondent layer

bluval.py was modified to reflect the changes

TODO: each layer under *tests* folder should have a correspondent
layer in the *docker* folder

Signed-off-by: Cristina Pauna <cristina.pauna@enea.com>
Change-Id: Ifdd46ee22b6d009eb17475c5e2efd8bd9f37c3ad