GCE-CoreOS: Fix etcd peer addresses

Inject master's peer-address into the minions' peer lists.

This bug fix is brough to you by some YAML dark magic and the
concatenation of config files in util.sh.  This allows us to avoid
processing the cloud-configs with a templating system, for now.
GCE-CoreOS: Override kubelet's hostname detection

Force the kubelet to listen on an etcd path based on its
non-fully-qualified hostname.

This fixes an issue that prevented the minions from receiving commands
from the master.

Baground: The master's "--cloud_provider=gce" kubelet identification
logic doesn't work on the GCE CoreOS image.  It fails to separate the
specific hostname from the rest of the FQDN.  The result is that the
master publishes events to an etcd path that includes just the machine
name, while the kubelet tries to listen on a path based on the FQDN.

See also: PR #584
GCE-CoreOS: Set the default minion count to 3