puppetboard/app.py: Using the plain-text metric name in metrics() (#259)

This fixes #258

URL quoting is now done in pypuppetdb >= 0.2.3 which contributed to the
metric URL being double-quoted by the time it reached PuppetDB, which
responds with a 404. Instead using the plain-text name to build the
link to metric()

puppetboard/app.py

@@ -771,10 +771,8 @@ def metrics(env):
     check_env(env, envs)
 
     metrics = get_or_abort(puppetdb._query, 'mbean')
-    for key, value in metrics.items():
-        metrics[key] = value.split('/')[2]
     return render_template('metrics.html',
-        metrics=sorted(metrics.items()),
+        metrics=sorted(metrics.keys()),
         envs=envs,
         current_env=env)