Switch to oslo.db and fix cmd.manage

This change doesn't remove all of the d.sqla.* modules for compat so we don't
need to change more things then needed. Things like multiple engines etc are
supported via a _FACADE dict in d.sqla.session and other things we need as
well.

We remove d.o.common.db code since it is not needed anymore and technically
replaced by oslo.db.

Notably the *biggest* change is changing database_connection to connection.

Also fixes problems with arguments in cmd.manage

Change-Id: I948a42b7f3dbc1d484200e86b3f8d0b85769ad08