[Minor] Fix style, formatting and naming in BlockManager etc.

This is a precursor to a bigger change. I wanted to separate out the relatively insignificant changes so the ultimate PR is not inflated.

(Warning: this PR is full of unimportant nitpicks)
This one might be nicer to break out:

```
val cmId = new ConnectionManagerId(peer.host, peer.port)
val putBlock = PutBlock(blockId, data, tLevel)
val syncPutBlockSuccess = BlockManagerWorker.syncPutBlock(cmId, putBlock)
```

That's the same number of lines and it's more clear.