Update to dbxtool 8
    
    - Make a "make coverity" rule to scan the source
      Results at: https://scan.coverity.com/projects/rhboot-dbxtool
    - Don't try to apply anything if PK and KEK aren't enrolled
    - Add --force and --quiet for the PK/KEK checker, and use them in the
      systemd service.
      Resolves: rhbz#1489942
    - Add a .syntastic_c_config for vim's Syntastic modules
    - Use tsearch()/tfind()/tdestroy() from libc instead of ccan htables
    - Don't open the dbx file with O_RDWR|O_CREAT, use O_RDONLY.
    - Lots of minor bug fixes gcc -Wextra and friends found.
    
    Signed-off-by: Peter Jones <pjones@redhat.com>