Rearrange db tests in prep for testr.

The way discover does test discovery will find any classes that subclass
the unittest base class. This means that db.base was getting picked up as
a set of tests that need to be run, which is bogus, as it's intended to just
be a base class.

Split it up a little bit differently to make it work as intended when
python test discovery is run outside of how nose things of things.

Part of blueprint grizzly-testtools

Change-Id: Iede92452d0c48224a1f80288c2bf2693224dc56f
Encrypt scrubber marker files

Files written to scrubber_datadir can contain credentials in plain text.

Update schedule_delayed_delete_from_backend to make use of
metadata_encryption_key to encrypt the uri before writing it out.

Fixes LP Bug #1112586

Change-Id: I03ff36f6b57f58a5e5de28bf8d48e7ce0216e5b3
Update HACKING.rst per recent changes

Added "is not" usage with examples
Fixed "not in" usage description
* https://review.openstack.org/#/c/20877/

Change-Id: I89fbc62a8b31bc7ef750cc1e80f73b9c1e366fd3
Merge "Rearrange db tests in prep for testr."
Merge "Update HACKING.rst per recent changes"
Merge "Encrypt scrubber marker files"