Enable using reputation metric for selection

[braydonf]

Now that we have a reputation metric being collected, it will be useful to use this for mirror selection instead of timeoutRate as it is currently. There are also a few other places that can be updated.

• https://github.com/Storj/bridge/blob/master/lib/server/routes/frames.js#L325
• https://github.com/Storj/bridge/blob/master/lib/server/routes/reports.js#L153
• https://github.com/Storj/bridge/blob/master/lib/monitor/index.js#L96

[braydonf]

Related: #526