feat(coreos/base): accept keywords on docker 0.7

we want docker 0.7, accept it's unstable nature
feat(coreos/base): add lvm thin
feat(coreos-devel/sdk-depends): add boost-build

building boost requires that the SDK has the b2 command line utility
installed in /usr/bin/b2. Install this utility in the sdk.
feat(accept_keywords): boost build is needed by lvm
Merge pull request #268 from philips/docker-0.7

feat(coreos/base): changes for docker 0.7