stage1/init: mirror host's /etc/localtime symlink target in rootfs

This suppresses the warning when systemd-nspawn tries recreating the host's
/etc/localtime symlink in the container filesystem.
Merge pull request #226 from vcaputo/mirrorlocalzoneinfo

stage1/init: mirror host's /etc/localtime symlink target in rootfs
vagrantfile: add support for local rocket development