bump(sys-kernel/coreos-kernel): to 3.10.4

- bump to the latest stable - 3.10.4
- add some minimal real hardware support
- modify cros-workon to allow EGIT_BRANCH to be set
Merge pull request #147 from philips/bump-to-3.10.4

bump(sys-kernel/coreos-kernel): to 3.10.4