hadrian: make it possible to run the testsuite with quickest and quick
hadrian: make it possible to run the testsuite with quickest and quick

More generally, we so far assumed that the testsuite would be executed
with a flavour that's as comprehensive as perf in terms of available RTS
and library flavours (at least vanilla + dynamic + prof). This would
manifest itself concretely by needing 3 "ways" of the iserv program,
unconditionally.

We now only require the ways among vanilla, dynamic and prof that we
can find in our current Flavour's rtsWays.

Test Plan:
hadrian/build.sh --flavour={quick, quickest} test now goes through
(with a few failing tests, of course).

Reviewers: bgamari, tdammers

Reviewed By: tdammers

Subscribers: mpickering, RyanGlScott, rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5355

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc