remove user_default_password from zvmsdk config

VMs created by ZCC are all LBONLY. The user_default_password is not used by zcc code, should remove it from config.

Together with this, some minor changes to config.py:

recommend values:
logging.ERROR: level above ERROR will be written to log file.
logging.WARNINS: level above WARNING(ERROR, WARNING)
                 will be written to log file.
logging.INFO: level above INFO(ERROR, WARNING, INFO)
              will be written to log file.
logging.DEBUG: All log level (ERROR, WARNING, INFO, DEBUG)
               will be written to log file.

logging.WARNINS should be LOGGING.WARN