Replace EC2 image/snapshot based with Elasticsearch snapshot based backup

[sopel]

This depends on #320 - Elasticsearch 1.0 features a dedicated backup/restore mechanism, see Introducing Snapshot & Restore:

With most/all instances being auto deployed and scaled anyway, the current catch all approach is more of a simple stop gap measure than a reasonable and scalable backup process, which should primarily be concerned with the data.

:information_source: on top of that it might also address related scaling and resilience issues:

We are very excited about this new feature. We like to think of incremental backup as a time machine for your data. We are confident that everyone who relies on Elasticsearch as a critical component in their system and cannot afford down time for re-indexing will find the new Snapshot and Restore mechanism really helpful. [emphasis mine]

This relates to e.g. #272/#273 and esp. #313 accordingly - @dpb587, @mrdavidlaing: I've been planning to summarize my thoughts around the implicit and explicit usage (or current lack thereof) of the Event Sourcing pattern within our cluster for over a week, but didn't get around to it yet - so in an extreme nutshell (there's much more to it, and as always a few issues as well):

• an explicit event sourcing approach would e.g. facilitate Apache Kafka/S3 to record the events and make them available for replay in restore and scaling operations
• depending on the use case, this pure version often doesn't scale
• therefore it is usually desirable to start from an interim pre processed state, and that's what @dpb587 is currently experimenting with via the EBS volume reuse in fact
• :interrobang: accordingly, the new incremental backup/restore functionality might allow to achieve just that in a reliable and scalable way?!

[sopel]

Closed as Won't Fix due to project being retired to the CityIndex Attic.