(#1997) - parse user agent for the perf tests

This gives us something like e.g.

```js
{ browser: 
   { name: 'Chrome',
     version: '34.0.1847.116',
     major: '34' },
  device: {},
  engine: { name: 'WebKit', version: '537.36' },
  cpu: {},
  os: { name: 'Mac OS X', version: '10.8.5' },
  userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/34.0.1847.116 Safari/537.36' }
```