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.

test/suites/encoding-flags/run

@@ -14,7 +14,7 @@ run_test() {
         if [ -f $test_path/env ]; then
             . $test_path/env
         fi
-        $json_process <$test_path/input >$test_log/stdout 2>$test_log/stderr
+        $json_process --env <$test_path/input >$test_log/stdout 2>$test_log/stderr
     )
     valgrind_check $test_log/stderr || return 1
     cmp -s $test_path/output $test_log/stdout