Change GDP_INSTALL_ROOT to GDP_ROOT, since all of the scripts in
$gdp/adm are looking for that name. An even better choice would be
GDP_RUN_ROOT, but we'll survive.
Rationalize macro names to avoid confusion and for consistency with the
base GDP code:
* GDP_ROOT => GDP_INSTALL_ROOT
* GDPROOT => GDP_SRC_ROOT
* GDPADM => GDP_ADM
Extensive rework on mqtt-gdp-gateway startup scripts. Not yet complete.