Fix some typos in neutron/db and IBM SDN-VE plugin

For example, in neutron/db/agents_db.py, db_plugin_base_v2 should be changed to db_base_plugin_v2.
There is no bug or blueprint related to this fix.

Change-Id: I0d348d92c9c32f172d1e505cf660aed4d064a440
Merge "Fix some typos in neutron/db and IBM SDN-VE plugin"