Remove unneeded layer from the DB interface

Since we are only going to support one database backend (sqlalchemy) we
can remove a lot of unnecessary code.  If some day we plan to support
more storage backends, we atleast know the code works.

Change-Id: I6e3d9a7be14dd5709329a71ba06bc1de0b45c314
Signed-off-by: Paul Belanger <paul.belanger@polybeacon.com>