check_apt_upgrade: replace [ -o ] by [ ] || [ ] as the former is deprecated in POSIX 2008
check_conntrack: replace [ -a ] by [ ] && [ ] as the former is deprecated in POSIX 2008
check_blkstat: replace [ -o/-a ] by [ ] ||/&& [ ] as the former is deprecated in POSIX 2008
check_apt_upgrade check_conntrack: update copyright year