parallel regression test output

There is something slightly funny about the regression test output.
When it starts a parallel group, it prints something like

parallel group (14 tests): select_views portals_p2 rules foreign_key
cluster dependency guc bitmapops combocid tsearch tsdicts foreign_data
window xmlmap

One would think that it prints this as the tests are started, but it
actually prints it as the tests finish. The last one or two test names
are always printed after a considerable delay, probably because of
terminal timing issues, which I have found confusing on several
occasions.

Note also that that behavior is inconsistent with that of a serial test
like

test misc ... ok

Here, the first part of the line is printed before that test starts, and
the result is printed after.

I propose to adjust the behavior so that the "parallel group" line
prints the test names before/as the tests are started, and then the
subsequent lines print the results after the tests finish, as is
currently the case.

See attached patch.