Add explicit ORDER BY to a few tests that exercise hash-join code.

A proposed patch, also by Thomas and in the same thread, would change
the output order of these.  Independent of the follow-up patches
getting committed, nailing down the order in these specific tests at
worst seems harmless.

Author: Thomas Munro
Discussion: https://postgr.es/m/CAEepm=1D4-tP7j7UAgT_j4ZX2j4Ehe1qgZQWFKBMb8F76UW5Rg@mail.gmail.com