This MR adds gitlab.com/gitlab-org/gitlab-pages/internal/jail
which implement a wrapper for building a chroot jail with file copy
and directory mount binding.
On top of that gitlab-pages chroot deamon will now create a complete
jail with /etc/resolv.conf, a copy of SSL_CERT_FILE placed in
/etc/ssl/ca-bundle.pem, and a bind mount of pages-root on /pages.
SSL_CERT_FILE can be provided by omnibus, see relevant documentation.
Closes #86 (closed)