Issue 1102: Fixup test suite, fix broken tests

A recent PR broken the JsonChecker tests by adding support for trailing
commas. This didn't end up breaking the build, because those tests
aren't run, except locally and only using CMake.

This patch fixes the tests by adding exclusions for trailing comma
tests, as well as updates Meson to run these tests as part of `ninja
test`.

See issue #1102.

meson.build

@@ -105,3 +105,13 @@ test(
     jsontestrunner,
     join_paths(meson.current_source_dir(), 'test/data')]
   )
+test(
+  'jsonchecker_jsontestrunner',
+  python,
+  args : [
+    '-B',
+    join_paths(meson.current_source_dir(), 'test/runjsontests.py'),
+    '--with-json-checker',
+    jsontestrunner,
+    join_paths(meson.current_source_dir(), 'test/data')]
+  )