Revert "Merge pull request #289 from waigani/manual-prov-key"

This reverts commit 2d129e3705fb738e25a16e1c34778f3083fb8450, reversing
changes made to a5ae823af408136787cd4abc574e0c2c18ba85ba.
Merge pull request #521 from waigani/revert-manual-prov

Revert "Merge pull request #289 from waigani/manual-prov-key"

This reverts commit 2d129e3705fb738e25a16e1c34778f3083fb8450, reversing
changes made to a5ae823af408136787cd4abc574e0c2c18ba85ba.
Issue #1357033: make a backups test more deterministic.
Merge pull request #525 from ericsnowcurrently/fix-1357033-broken-backups-test

Issue #1357033: make a backups test more deterministic.

Here is a solution to the failing test from [issue #1357033](https://bugs.launchpad.net/juju-core/+bug/1357033).  Incidentally, I took this basically verbatim from one of my outstanding PRs.
Add a backups config abstraction.
Add an abstraction for state-relevant paths.
Add tests for DBConnInfo.
Add a DB info abstraction for backups config.
Add tests for BackupsConfig.
Remove some superfluous comments.
errors.Errorf -> errors.New