fix(coreos-base/coreos): Switch awk implementation to gawk.

Space saving by using mawk is not significant and a number of things
depend on gawk so save us the trouble and just switch.
fix(coreos-base/coreos-dev): Add gentoolkit (includes equery)

I keep wanting this tool, so here it is!

Add explicit dependency on portage just to be clear that it is in the
dev image, not the base image.
remove(coreos-base/dev-install): Remove oddball portage configuration.

Now that dev images install packages into root instead of /usr/local we
can move to configuring portage in those images in a more standard way.
We also don't support turning a prod image directly into a dev image so
this sort of stuff doesn't belong in the base system anyway.
Merge pull request #223 from marineam/dev-updates

Dev updates