coverage: Bring test_templates.py to 100% coverage.

tools/test-backend

@@ -87,7 +87,6 @@ not_yet_fully_covered = {
     'zerver/tests/test_decorators.py',
     'zerver/tests/test_email_mirror.py',
     'zerver/tests/test_narrow.py',
-    'zerver/tests/test_templates.py',
     'zerver/tests/test_tornado.py',
     'zerver/tests/test_urls.py',
     # Getting views file coverage to 100% is a major project goal

zerver/tests/test_templates.py

@@ -124,7 +124,7 @@ class TemplateTestCase(ZulipTestCase):
             template = get_template(template_name)
             try:
                 template.render(context)
-            except Exception:
+            except Exception:  # nocoverage # nicer error handler
                 logging.error("Exception while rendering '{}'".format(template.template.name))
                 raise