GitLab

Currently keys that get logged are casted from []byte. Which means that log output looks like this.
```
{"event":"getClosestPeersBegin","key":"\u0012 \ufffdᱡ\ufffd`\ufffdF]\ufffd\ufffdᠸCƶ\u0006E\ufffdrb\ufffd\ufffdO\ufffd\ufffdu\ufffd\ufffdj\u000b","system":"dht","time":"2017-07-27T11:12:08.51775836Z"}
```
after fix like this:
```
{"event":"getClosestPeersBegin","key":"QmQyyaB8znrakGydP3ynRsXre96Uw9wc6w6zuP61bbZuNj","system":"dht","time":"2017-07-27T11:16:30.693008112Z"}
```