Remove dependency from docker/pkg/systemd

Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com>
Merge pull request #159 from LK4D4/remove_docker_systemd_dep

Remove dependency from docker/pkg/systemd
Added support for Libseccomp syscall filtering

Vendored golang-seccomp bindings for libseccomp added, as is a build dependency
on libseccomp version 2.1 or higher.

Signed-off-by: Matthew Heon <mheon@redhat.com>