Class usage came from the unittest framework and it was always redundant
after migration to the pytest. This commit removes classes from files
containing tests to make them more readable and understandable.
Prerequisites check moved to the module level to simplify class structure.
Discovery and prerequisites checks functions moved to the separate files.
Introduced "require" fixture to provide per-test requirements check.
Common methods from applications/proto.py converted to the fixtures.
sysctl check moved to the specific file where it is using.
Some options moved to the constructor to have early access.
To make fixtures accessible inside of setup methods in tests all these methods
are renamed to the "setup_method_fixture" and decorated by autouse flag.
Also all setup methods moved to the top of the files.
