- fixed getSingleInstSourceSatSolvable()
  * instead of rely on the suffix of a file it's better to
    actually check if it's compressed or non compressed data
    due to redirections and symlinks it might happen that a
    file name e.g 'packages' is resolved into 'packages.en.gz'
    kiwi downloaded the file and failed to check that it's
    a compressed file (bnc #822247)