logger: behave nicely as a library, configure resultsdb_api logger
    
    This improves behavior when libtaskotron is not used as the main script,
    but as a library. It no longer configures libtaskotron logger to the
    DEBUG level by default, but inherits the root logger configuration. That
    allows script authors to tune logging verbosity in a central place and
    libtaskotron will respect that.
    
    If libtaskotron is used as the main script, we set maximum verbosity and
    then control the messages in the handlers.
    
    Resultsdb_api is now also set to maximum verbosity when libtaskotron is
    running as the main script. This allows us to see resultsdb_api errors
    and debug messages during task execution.
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D314