Print SpecFile parsing debug info
    
    The recently added class SpecFile parses a specfile with tool rpmspec.
    It provides error messages when parsing failed. This change will show
    these messages to user. Without this rhpkg only fails with exception
    and simple message.
    
    Resolves: rhbz#2000556
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>