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/valid/complex-array/env

@@ -0,0 +1 @@
+JSON_SORT_KEYS=1

test/suites/valid/run

@@ -19,7 +19,7 @@ do_run() {
     strip=0
     [ "$variant" = "strip" ] && strip=1
 
-    STRIP=$strip $json_process \
+    STRIP=$strip $json_process --env \
         <$test_path/input >$test_log/stdout$s 2>$test_log/stderr$s
     valgrind_check $test_log/stderr$s || return 1