TICKET-647: Fix unselected output verbosity in py test groups

[Naragod]

Description

Saving autotest settings fails for Python test groups. The form shows two errors on the group:

• must be equal to one of the allowed values under Output verbosity
• must match exactly one schema in oneOf on the group as a whole

PyTestData sets output_verbosity to "" at runtime. generate_schema copies that sentinel into the JSON Schema as default, so the form seeds the field with "" before the tester dependency picks a branch. The pytest branch accepts short, auto, long, no, line, and native. The unittest branch accepts 0, 1, and 2. Neither lists "". The field breaks its own enum, and the group then matches neither branch, which raises the oneOf error.

Implementation

• Drop the base default for output_verbosity in server/autotest_server/testers/py/setup.py such that the form seeds the field from the matched branch instead.
• Leave the branch defaults alone: short for pytest, 2 for unittest.

Note

Fixes MarkUs issue 8129.