[6.14.z] Fixture collection splitting restructured

[Satellite-QE]

Cherrypick of PR: #12923

The processing of the list of fixtures in the command line for in Pytest Plugin Fixture Collection is restructured.

Earlier:

# pytest --uses-fixtures fix1 fix2 fix3 tests/foreman

Now:

# pytest --uses-fixtures fix1,fix2,fix3 tests/foreman

Issue and Fix:

Earlier pytest is used to process all the non specific arguments after --uses-fixtures option , e.g in example above it used to consider tests/foreman as fixture as well :)

Now, it process only a string after an option and splits string by comma to obtain the list of fixtures to collect the tests for all those fixtures.