Bump version to v0.9.15 for CoreOS Beta 367.1.0
Update README
Follow an incompatible change in CoreOS 379

- https://coreos.com/releases/#379.0.0
> Incompatible Change: QEMU/KVM based platforms change the virtio based network interface name from something like ens3 or ens4v1 back to the classic eth0, eth1, etc. names. This is because virtio device numbers (the v1 in ens4v1) are not any more predictable than the eth0 style names are.
Merge branch 'refs/heads/master' into alpha
Bump version to v0.9.18