[tests] Re-enable disabled test.
[tests] Re-enable disabled test.

 - This was failing because of non-determinism in the output due to
   the race conditions fixed in the last two commits. I verified the
   output is now stable over 100s of iterations on 14.04 (where it
   appeared most likely to fail).

apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild