[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)
Did not know that existed. Also, I did a grep for it and it looks like it's only used in 2 places, neither of which is in BlockManager.scala... I'll change that.