Disable Jinja2 template auto_reload for higher performance

Every time we run a JS behavior, we load a Jinja2 template.
By default, Jinja2 has option `auto_reload=True`. This mean that
every time a template is requested the loader checks if the source file changed
and if yes, it will reload the template. For higher performance it’s possible
to disable that.

Also note that Jinja caches 400 templates by default.

Ref: http://jinja.pocoo.org/docs/2.10/api/

In Brozzler, we don't make changes to JS templates while the system is
running. So, there is no point in having auto_reload=True.

brozzler/__init__.py

@@ -258,7 +258,7 @@ def jinja2_environment(behaviors_dir=None):
                                                            'js-templates'))
         else:
             _loader=jinja2.PackageLoader('brozzler', 'js-templates')
-        _jinja2_env = jinja2.Environment(loader=_loader)
+        _jinja2_env = jinja2.Environment(loader=_loader, auto_reload=False)
         _jinja2_env.filters['json'] = json.dumps
     return _jinja2_env