Provide a deterministic approach for resources requesting same hostname

Currently resources which request same hostname example.com will be interchangeably given DNS record on Route53 (possible Google DNS too). It can be resolved by creating deterministic approach - do not overwrite the record if it was created in Route53 and still required.

If we have to records: elb-aws-1.com requesting example.com and elb-aws-2.com requesting example.com, then we check with AWS Route53:

1. if there exists a record owned by Mate example.com: a. it is pointing to either elb-aws-1.com or elb-aws-2.com - no changes at all b. it is pointing to neither. Choose any of the two and create the record
2. If no record exists for example.com - pick any of the two

/cc @linki is there any issue regarding that in GKE ?

This is not (yet?) a deterministic approach, but the flow described above is addressed in this PR: https://github.com/zalando-incubator/mate/pull/74

I think it will create multiple A records with the same name pointing to different services. Neat, if you want it but bad if you don't.

Your solution makes sure that only one service is allowed per DNS name? (whoever is first wins?)

@linki since we are using upsert only, it will not create duplicates :) Yes for the question :)