Get configuration value from database table. If no value found user
    will be prompted to enter one.

    Parameters
    ----------
      configKey : string
        Name of config field.

      strDescriptor : string
        Description of config field.

      isDir : boolean [optional : default = True]
        Set to True if config value is
        expected to be a directory path.

    Returns
    ----------
      string
        Value for given config field in database.

def _GetConfigValue(self, configKey, strDescriptor, isDir = True):
    """
    Get configuration value from database table. If no value found user
    will be prompted to enter one.

    Parameters
    ----------
      configKey : string
        Name of config field.

      strDescriptor : string
        Description of config field.

      isDir : boolean [optional : default = True]
        Set to True if config value is
        expected to be a directory path.

    Returns
    ----------
      string
        Value for given config field in database.
    """
    goodlogging.Log.Info("CLEAR", "Loading {0} from database:".format(strDescriptor))
    goodlogging.Log.IncreaseIndent()
    configValue = self._db.GetConfigValue(configKey)

    if configValue is None:
      goodlogging.Log.Info("CLEAR", "No {0} exists in database".format(strDescriptor))
      configValue = self._UserUpdateConfigValue(configKey, strDescriptor, isDir)
    else:
      goodlogging.Log.Info("CLEAR", "Got {0} {1} from database".format(strDescriptor, configValue))


    if not isDir or os.path.isdir(configValue):
      goodlogging.Log.Info("CLEAR", "Using {0} {1}".format(strDescriptor, configValue))
      goodlogging.Log.DecreaseIndent()
      return configValue
    else:
      goodlogging.Log.Info("CLEAR", "Exiting... {0} is not recognised as a directory".format(configValue))
      sys.exit(0)