Refresh network info cache for secgroups

Before updating security group rules, we need to make sure that
the info cache is up-to-date. Without this source groups are not
updated properly. This was a regression introduced in commit
85aac04704350566d6b06aa7a3b99649946c672c which fixed a potential
DOS using source groups.

Fixes bug 1216720

Conflicts:
	nova/network/manager.py
	nova/tests/network/test_manager.py

Change-Id: I6b5115df53f2e159ea506ef966cd49cedd35f83d
(cherry picked from commit 8679b2c8e7f9fddc31a74ad00f6705bca00a762b)
Merge "Refresh network info cache for secgroups" into stable/grizzly