pkgbase: Move uuidgen to runtime package

This is useful to have a valid /etc/hostid and /etc/machine-id for
small mfsroot based setup and not needing to install FreeBSD-utilities

Sponsored by: Beckhoff Automation GmbH & Co. KG
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D42149

(cherry picked from commit 6a804af4c0e3ce3574e23695f587c11f5958bcbb)