Conditionally import ibmdb2/ibm_db_sa
Conditionally import ibmdb2/ibm_db_sa

Since ibm_db_sa is not part of sqlalchemy, we need to handle the
conditional import of the module in visitor.py so we don't get an
ImportError if ibm_db_sa is not available.

Closes-Bug: #1287229

Change-Id: Ida070b629ce3b9be727ae49973bb6a71543c1dcf

rcherrueau/sqlalchemy-migrate,openstack/sqlalchemy-migrate,rcherrueau/sqlalchemy-migrate,stackforge/sqlalchemy-migrate,dannon/sqlalchemy-migrate,openstack/sqlalchemy-migrate,andras-tim/sqlalchemy-migrate