Distribution/Gentoo/GHC.hs: speed up lookup of several broken packages

Before the patch we probed whole file system for _each_ unknown broken package
(effectively grepped for foo.conf).

After the patch we try to locate all the corresponding
packages for all '*.conf' files in one run.

The performance problem is seen nicely on 500 broken packages.

Before the patch haskell-updater spinned for about 5 minutes,
now it takes 7 seconds (hot filesystem cache).

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Update options as cave resolve doesn't have --quiet option

REPORTED-BY: L29Ah_.