Improve expectation.
Remove inconsistent #order and #randomize? config methods.

* Examples and groups can be ordered differently.
* Individual groups can be ordered differently.

As such, a global `order` reader method doesn't
make a lot of sense (although, assigning the global
default via `#order=` still does, I think).

Also:

* This exposed that the ordering force logic
  (e.g. to ensure CLI `--order rand` takes
  precedence over `RSpec.configure`) didn't
  work properly since it simply ensured `order`
  returned the forced option but did not ensure
  the global ordering was set properly.  I've
  fixed this.
* Don't clear the seed when setting the order to
  default. An individual example group may still
  be run in random order and will need the seed.
  There's really no reason to clear it.
* Always print the seed at the end of the run,
  even if default order is used. Consider that
  only one group may be randomized, in which case
  the seed would be important. Ideally, I'd like
  to refine this further so that it is conditionally
  printed based on if the random orderer ever got
  used, but that can be a later commit.