nova/db/__init__.py was importing * from nova.db.api. This meant that
any time any code anywhere within the nova.db package was imported
then nova.db.api was too, leading to a cascade of imports that may
not have been desired. Also, in general, code in __init__.py is a pain.

Therefore, this change adjusts code that so that either:

* nova.db.api is used directly
* nova.db.api is imported as 'db'

In either case, the functionality remains the same.

The primary goal of this change was to make it possible to import the
model files without having to import the db api. Moving the model files
to a different place in the directory hierarchy was considered, but
given that "code in __init__.py is a pain" this mode was chosen.

This looks like a very large change, but it is essentially adjusting
package names, many in mocks.

Change-Id: Ic1fd7c87ceda05eeb96735da2a415ef37060bb1a

In Liberty, we converted to using the manifest-based class
action and backport methods, which no longer rely on these
object relationship maps. They provide a full manifest of
client-side versions with each call, which is far more
robust than us trying to hand-edit these mappings (which
we get incorrect a lot).

Since we're now in Mitaka, we can drop compatibility with
clients that don't make the version-manifest calls. Those
have also been deprecated in oslo.versionedobjects.

Change-Id: Iea8b6348e3b01aaa335ec5408f07826f1e758d20

List objects used to use child_versions, which was tested in a more
shallow way than test_relationships() tests obj_relationships. This
change moves over all list classes to use obj_relationships (and
therefore are now tested in test_relationships() with all other
objects).

Change-Id: I334dba243de45bf11ccb5ab55e2aa8390fe9d8c2
Closes-Bug: #1470154

This change adds a TaskLog object to replace calls currently proxying
through conductor.

Related to blueprint liberty-objects

Change-Id: I4249f38cd8b9c23c2cc320838c622e82aae54f16