Always output run options, which include the seed used

This is important because of Minitest's random ordering-- if there are
bugs that occur in some orderings, being able to run with the same seed
to reproduce the same ordering is essential.

This was added to minitest-reporters once before, in df651b0, but looks
like it didn't survive the 1.0 refactoring :) Discussion when that was
added: https://github.com/kern/minitest-reporters/pull/55/files