Improve performance of security group DB query

Improve performance of security group DB query

The _select_ips_for_remote_group method was joining the
IP allocation, port, allowed address pair, and security group tables
together in a single query. Additionally, it was loading all of
the port columns and using none of them. This resulted in a
very expensive query with no benefit.

This patch eliminates the unnecessary use of the port table by joining
the IP allocation table directly to the security groups and allowed
address pairs tables. In local testing of the method, this sped it up
by an order of magnitude.

Closes-Bug: #1373851
Change-Id: I12899413004838d2d22b691f1e2f3b18f7ec2c27