Issue 50984 - Memory leaks in disk monitoring
    
    Description: Memory leaks are reported by the disk monitoring test suite.
    The direct leak is related to char **dirs array which is not freed at all.
    Free the array when we clean up or go to shutdown.
    Fix disk_monitoring_test.py::test_below_half_of_the_threshold_not_starting_after_shutdown.
    It should accept different exception when the instance is not started.
    
    https://pagure.io/389-ds-base/issue/50984
    
    Reviewed by: firstyear (Thanks!)