Reorganize tests/ util code

It's nicer to have a separate tree for stuff we're importing
vs actual tests.
Remove DB() fixture from conftest.py

Deprecated by new fixture in util/base.py.
Note about what goes in conftest.py
Document expected behaviour instead of leaving XXX comment
Test fixture for API clients
Make test_api.py use new api_client fixture
Use different ports for ZeroRPC services during testing

Otherwise we get port clashes if we have an instance running
and try to run tests.
Put test data dump in subdir.

More separating tests vs other test stuff.
Make TestDB get configuration from test config

We already have the config() fixture from conftest.py,
so we don't need to replicate it here. In the future
we may want to unify the fixtures in conftest.py with
this other tree of fixtures.
Don't import from within a method unless we have to.
configure message parts folder for testing
make ./inbox support specifying an alternative config file
Remove deprecated config variables
Specify rolodex server loc in test config
cleanups
Don't hardcode ZeroRPC service socket locations
more ignores
Update test data

We need parts too!
unify conftest.py and tests/util tree
Fix postel test