Upgrade failure for DB2 at ml2_binding_vif_details

50d5ba354c23_ml2_binding_vif_details fails during upgrade
when DB2 is used as the DB backend of neutron because
Boolean type is not supported by DB2.

This fix uses "1" instead of "true" in sql when db2 is engine.
This fix also changes context creation to op.execute.

Change-Id: I82d2141007894342c634f2c5e62344e20d876d8f
Closes-Bug: 1311589
Merge "Upgrade failure for DB2 at ml2_binding_vif_details"