Agent management extension

1/3 part of blueprint quantum-scheduler

This patch adds agent management support
to l3-agent and plugin-agent (ovs and linuxbridge).

Change-Id: Iebc272f45c7530c995f32ef3729b11cd76779385
Fix SG interface to reflect the reality

The signitures of abstract methods in SecurityGroupPluginBase
has diverged from db mixin implementation.
This patch updates the methods to fix the divergence, mainly
by removing update method from the base. Note that there's an
issue for missing update(bug #1124865).

Fixes: bug #1119080

Change-Id: I6631b86ab2fdf4b81ad575e9a8f92dfe041ffe9a
Signed-off-by: Tomoe Sugihara <tomoe@midokura.com>
Merge "Agent management extension"
Merge "Fix SG interface to reflect the reality"