pkg: Use NO_ROOT and WITHOUT_QEMU for release make invocation

[emaste]

Summary

The pkg build invokes `make -V BRANCH` in release/ to choose the
appropriate FreeBSD.conf filename.  We are moving to building all
release artifacts in NO_ROOT mode (which also requires WITHOUT_QEMU).

For testing, some work in progress produces an error if NO_ROOT is not
set in release/.  Set the flags here to avoid tripping over that.

[cperciva]

I have no objection to this change, but is the erroring-out you mention still an issue after b485322d6b5846fe4fb5aff6c4a07221b09946fc ?

[emaste]

bsdinstall too

[emaste]

The "work in progress" alluded to in the commit message is not yet committed, but maybe I just need to make a similar change to b485322d6b58 locally.