Add metadata for state backups.
Remove superfluous code and track backup origins.
Add an extra backup timestamp field and rename a file.
Fix docstrings.
errors.Errorf -> errors.Annotate
Fix a copy-and-paste docstring issue.
Test for the actual env ID rather than a bad regex.
archived -> stored
backup -> backups
Fix formatting.
Panic if we cannot find the hostname.
Fix some typos.
Clean up backups metadata test code.
Rename the mongo collection for backups metadata.
Use ConnSuite instead of StateSuite.
Merge pull request #453 from ericsnowcurrently/backups-metadata

Add metadata for state backups.

This is part of my effort to split up the work for backups into a few smaller patches.