fix(coreos-base/coreos-init): Move daemon setup to init package.

Previously coreos-base handled some sshd and dhcpcd and lacked the
dependencies required to make enabling systemd units work. coreos-init
is a better place for that and has a proper source package so fewer
files are needed in the portage overlay.
bump(coreos-base/coreos-init): Update to latest code version.

This adds the new sshd-keygen unit.
fix(systemd-rest+docker): Use keepdir to install empty /var directories.

Not only is this the safer way of installing empty directories but we
can now leverage keepdir to repopulate missing items in var.
bump(coreos-base/coreos-init): New code

Adds tmpfiles config, more units, and top level coreos-startup.target
which eliminates the need for maintaining that list in the ebuild.
fix(coreos-base/coreos-base): Remove dummy rootfs entry from fstab.

Remounting / read-write has been moved to the dev_mode helper script in
coreos-init instead of letting systemd do it based on fstab. Now if a
system boots without /root/.dev_mode the filesystem remains read-only.
bump(coreos-base/coreos-init): config update
Merge pull request #7 from marineam/boot-cleanup

Boot cleanup