Implemented plugin.update_port (DB schema changes!)

* Updated models.Port to include name, admin_state_up, device_owner
* Implemented update_port attributes:
  - name
  - admin_state_up
  - fixed_ips
  - device_id
  - device_owner
Merge pull request #58 from asadoughi/update_port

Implemented plugin.update_port (DB schema changes!)