Issue 49381 - Refactor numerous suite docstrings - Part 2
    
    Description: We need to have properly formatted and detailed
    docstrings in all existing test suites.
    Suites that were changed in this commit:
    sasl allowed_mechs, basic, password, replication.
    Also, fix create test.py tool, create password policy fixture in
    syntax test, in replication move get_repl_entries to __init__.py,
    move test_double_delete, test_password_repl_error, test_invalid_agmt
    from acceptance_test.py to regression_test.py.
    Rename plain.py to plain_test.py
    and allowed_mechs.py to allowed_mechs_test.py.
    
    https://pagure.io/389-ds-base/issue/49381
    
    Reviewed by: amsharma, vashirov, wibrown (Thanks!)