release: Make azure cloudware images buildable as non-root

• Don't chroot to uninstall pkg since we don't install pkg in the first place.
• Use pw -R instead of chrooting.
• Add metalog entries.

Reviewed by: cperciva, emaste
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D52451