There have been a few changes over the past few months, here we make the
following changes.
* change from backtrack=99 to complete-graph as a more correct flag
* make python version selection more in line with what gentoo supports
* set up python before stuff gets pip installed
* ensure we have the proper pip so we can install pip packages as root
* ensure we have the proper use flags for the disk formatting changes
* set DIB_RELEASE like other distros
* fix openssh-server element for gentoo
Change-Id: I17202de3016616ce34c8cbead7d0fb047a64e96b
