D16592: [ExtractorCollection] Add unit-test to verify only specific extractor is used

[Stefan Brüns]

bruns added a dependent revision: D16593: [ExtractorCollection] Use only best 
matching extractor plugin.

REPOSITORY
  R286 KFileMetaData

REVISION DETAIL
  https://phabricator.kde.org/D16592

To: bruns, #frameworks, astippich
Cc: kde-frameworks-devel, #baloo, ashaposhnikov, michaelh, astippich, spoorun, 
ngraham, bruns, abrahams