virt: Cartesian config update v3 without exclude filter.

Version without exclude filter was created because exclude filter code need more discussion.

repaired indentation problems which were commented in https://github.com/autotest/virt-test/pull/252

Features:

    virt: Adds possibility filter defaults variant from variants
    virt: Adds named variants to Cartesian config.

Unittest:

    virt: Update cartesian config unittest
    virt: Update Cartesian config unittest named variants
    virt: Update Cartesian config unittest default variants. 
   

Debug:

    virt: Make Cartesian config more verbose
    virt: Adds formal definition for Cartesian config