Revert "Remove sd_journal_open_container as it's not in systemd 208 and isn't used"

This reverts commit 4c433217b565bbb03bbbb8fdcc1017c673bbb3fa.
Systemd::Journal.new(container: 'foo') uses the
sd_journal_open_container call.
fix support for systemd 208 which doesn't have sd_journal_open_container