fix(dev-db/etcd): Require c10n, start even if cluster config is missing.

If c10n fails etcd should not start, wait until it is known if there is
a cluster config to use or not. Also now c10n may not write out a
cluster config on ec2 if there isn't a need for one. Make this case
non-fatal and start up etcd as a master node.
bump(coreos-base/coreos-init): Grab fixed c10n script.