scpi-dmm: add "switch to local" support for Agilent protocol
Send "SYST:LOC" to Agilent protocol speaking scpi-dmm devices at the end
of the probe (--scan) as well as in close (--show, --samples, etc). This
ends "remote" and re-enters "local" mode after programmatic use. Should
increase usability, eliminates the need for manual intervention before
subsequent DMM use. Was tested with a Keysight DMM. Does not affect the
HP protocol speaking devices.