Create custom JSONEncoder to stringify Exceptions

test/sanity/validate-modules/validate-modules

@@ -69,6 +69,14 @@ BLACKLIST_IMPORTS = {
 }
 
 
+class ReporterEncoder(json.JSONEncoder):
+    def default(self, o):
+        if isinstance(o, Exception):
+            return str(o)
+
+        return json.JSONEncoder.default(self, o)
+
+
 class Reporter(object):
     @staticmethod
     @contextmanager
@@ -135,7 +143,7 @@ class Reporter(object):
         ret = [len(r['errors']) for _, r in reports.items()]
 
         with Reporter._output_handle(output) as handle:
-            print(json.dumps(Reporter._filter_out_ok(reports), indent=4), file=handle)
+            print(json.dumps(Reporter._filter_out_ok(reports), indent=4, cls=ReporterEncoder), file=handle)
 
         return 3 if sum(ret) else 0
 
@@ -505,7 +513,6 @@ class ModuleValidator(Validator):
                 else:
                     self.warnings.append(msg)
 
-
     def _find_ps_replacers(self):
         if 'WANT_JSON' not in self.text:
             self.errors.append((206, 'WANT_JSON not found in module'))