storage, etcd: remove backend

[maiqueb]

Fixes: #231

This is a breaking API change.

[coveralls]

Pull Request Test Coverage Report for Build 2690322800

• 5 of 9 (55.56%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+5.8%) to 65.053%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/config/config.go	1	5	20.0%

Files with Coverage Reduction	New Missed Lines	%
cmd/whereabouts.go	1	77.53%
pkg/config/config.go	1	55.29%

Totals
Change from base Build 2656571269:	5.8%
Covered Lines:	927
Relevant Lines:	1425

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💛 - Coveralls

[dougbtv]

Miguel and I discussed the method by which we're removing the etcd support, with the consideration of "what if we add another backend in the future?" -- the outcome as suggested by Miguel was that we should expose the API in such way as to not need the handler as it's used today, and I concur, it's a better approach.

[dougbtv]

Additionally -- it works in my lab ;) 👍

[maiqueb]

@dougbtv we need to make sure this change is listed in the release notes of the next release.