build: Check NO_ROOT and METALOG for more targets

In f6575ed0deb08 I added a check that DISTDIR is set and is not / for
make distributeworld. Extend the check to distributekernel and the
two package* targets as the same argument applies.

Reviewed by: brooks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48339