gather: Print profiling information to stderr
    
    On stdout it gets mixed with listing of gathered packages. This has no
    effect in a real pungi-koji run, where both streams are merged into a
    single file which is then parsed, but in manual debugging runs it's a
    little obnoxious.
    
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>