Add back the old ENV variabe approach to json_process.

Enable using the old envrionment variable passing of settings for json_process
so that the current autoconf test suite scripts can run nicely.

json_process now takes an optional command line parameter --env which
causes it to use the old method of reading the settings from
environment variables instead of directly from the "env" file.

Also added a --strip command line option, this will be used to
run the stripped tests with CMake as well.