Test error conditions.

Fix 412 template to use standard styling that the other 400 templates use.
Update forbidden error to return status code 403 instead of 400.

Signed-off-by: Mike Terzo <mike@terzo.org>

puppetboard/app.py

@@ -121,7 +121,7 @@ def bad_request(e):
 @app.errorhandler(403)
 def forbidden(e):
     envs = environments()
-    return render_template('403.html', envs=envs), 400
+    return render_template('403.html', envs=envs), 403
 
 
 @app.errorhandler(404)