Add helper to look for missing binaries
    
    Fedora has merged /usr/bin and /bin while Debian uses distinct
    directories for /usr/bin and /bin. Debian also uses different directory
    for libexec files.
    
    A new paths.check_paths() helper makes it easier to detect missing or
    wrong paths.
    
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>