Feature/external etcd

[pieterlange]

Work in progress for pointing the kube cluster to an externally managed etcd cluster.

To disable the discrete etcd cluster 'embedded' in kube-aws, set the following parameters:

# Set this value to the full HTTP/HTTPS endpoint of your existing etcd cluster or leave commented to build a new cluster as part of this stack.
#etcdLoadBalancer: "http://my.etcd.cluster.local:2379"
#etcdSecurityGroups: [ "sg-abcdefg", "sg-1234567" ]

etcdLoadBalancer is a stable address to find the etcd cluster on, in many cases an ELB.
One must set etcdSecurityGroups in order to automatically add SecurityGroupIngress resources to said securitygroups, allowing the kubernetes components access on port 2379.

This is highly volatile code. 💣

Ref: #27

[codecov-io]

Current coverage is 56.28% (diff: 61.90%)

Merging #32 into experimental/external-etcd will decrease coverage by 0.61%

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