Add two new configuration options for metrics:
    value_as_label: string
        Given a label name the read value will be exported as value for
        this label. Metric's value is set to 1
    value_emun: list of strings
        Given a list of possible values a metrics line for all this
        values as values for label from value_as_label is exported.
        the line with the matching value is seet to 1 all others are 0.