update os_base to 7.x-2.x branch

I've created a 7.x-2.x version of os_base (https://github.com/opensourcery/os_base/tree/7.x-2.x). Please review and test that first, then if things are good, make a note here and we can update turnip to look at it.  This is sort of an intermediary step prior to moving os_base into turnip.