Merge these, removing an unnecessary layer of abstraction, and place
them in the new 'nova.db.main' directory. The resulting change is huge,
but it's mainly the result of 's/sqlalchemy import api/main import api/'
and 's/nova.db.api/nova.db.main.api/' with some necessary cleanup. We
also need to rework how we do the blocking of API calls since we no
longer have a 'DBAPI' object that we can monkey patch as we were doing
before. This is now done via a global variable that is set by the 'main'
function of 'nova.cmd.compute'.

The main impact of this change is that it's no longer possible to set
'[database] use_db_reconnect' and have all APIs automatically wrapped in
a DB retry. Seeing as this behavior is experimental, isn't applied to
any of the API DB methods (which don't use oslo.db's 'DBAPI' helper),
and is used explicitly in what would appear to be the critical cases
(via the explicit 'oslo_db.api.wrap_db_retry' decorator), this doesn't
seem like a huge loss.

Change-Id: Iad2e4da4546b80a016e477577d23accb2606a6e4
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

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

We don't need to have the vi modelines in each source file,
it can be set in a user's vimrc if required.

Also a check is added to hacking to detect if they are re-added.

Change-Id: I347307a5145b2760c69085b6ca850d6a9137ffc6
Closes-Bug: #1229324

Wildcard imports make reading code unnecessarily confusing because they
make it harder to see where a functions comes from.  We had two types of
wildcard imports in the code. Unneeded ones in test files that are just
removed, and some that we actually want which are kept using the '#
noqa' comment to tell flake8 to skip specific checks (such as H303)
for that line.

Change-Id: Id4705011579659fd74a4aaa05ac541e9694c483e