Switch the pkg(8) repository to use the 11.0 release package set for
consistent DVD image creation.

This is a direct commit to releng/11.0.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy stable/11@r303970 to releng/11.0 as part of the 11.0-RELEASE
cycle.

Prune svn:mergeinfo from the new branch, and rename it to RC1.

Update __FreeBSD_version.

Use the quarterly branch for the default FreeBSD.conf pkg(8) repo and
the dvd1.iso packages population.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Update the pkg-stage target to be more compatible with pkg-1.2:

- Add a release-dvd.conf pkg(8) configuration file to override
the default FreeBSD.conf configuration.
- Remove architecture-specific pkg-stage.conf files, consolidate,
and move their contents to scripts/pkg-stage.sh.
- Use 'pkg -vv' to determine the ABI, which is used as the
cache directory.

Prior to these changes, it would be possible for pkg-stage to fetch
conflicting binary packages from multiple repositories.

Tested against: head@r260522, stable/10@r260522

MFC after: 3 days
X-Insta-MFC: possibly
Sponsored by: The FreeBSD Foundation