illumos gate

The zone brand support is currently spread around in ways that we've found inconvenient.
The common stuff is in illumos-gate, as is the S10 brand support, but the ipkg brand has
the zone brand scripts and such over in the ipkg gate. All these zone brand scripts
share rather intimate relationships with the common zone brand code, making it
somewhat cumbersome to work on them in separate source repositories.

This feature request is to integrate the ipkg zone scripts (and only those, not
the entirety of the tools from the ipkg gate) from here:
https://hg.openindiana.org/sustaining/oi_151a/pkg-gate/file/1ff317412fe4/src/brand

This will involve some follow-on changes for OI and other consumers so the
external gates don't try to build the same package twice. The package is:
pkg:/system/zones/brand/ipkg