Update to version 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.
• 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.