if db is empty, upgrade directly to the sqlalchemy model

We now have lots of versions. The initial install takes lots of time
especially for pg or sqlite on a slow disk

If we detect no versioning, we just use sqlaclhemy to create the tables from
the model

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
Merge pull request #1377 from tardyp/dbcreation

if db is empty, upgrade directly to the sqlalchemy model