churn(profiles): Move default/linux to coreos/base

Move all of the coreos stuff to coreos/base and a couple other places
while switching to the upstream version of default/linux. This needs
further cleanup but it sufficient for the transition.
churn(profiles): Move arch/amd64

The only CoreOS specific things in this profile appear to have been
a few use flags for the SDK. Switch to the upstream amd64 profile after
moving these flags around in the appropriate target profiles.

The one function change here is that the delta_generator use flag is now
properly disabled outside of the SDK as it was in chromeos.
churn(profiles): Move base to coreos/base.

Switch to upstream's base profile, moving coreos specific stuff into
coreos/base and elsewhere as needed. No significant changes but a lot of
use flag nose in this since things like the list of available python
targets changes.
fix(profiles): Add udev to the stage1 use flags.

Bootstrapping now pulls in udev which is provided by systemd, systemd
pulls in hwids which must have the udev use flag enabled. Also add
gentoo-systemd-integration which will be used with the next version of
systemd.
Merge pull request #218 from marineam/profiles

Profiles