Update migration defaults

In TripleO we wanted to enable live block migration. Pleasantly
surprising was finding that all it required was better options to
libvirt.

I'm told this works with the libvirt we gate on, though as we don't
gate migration yet, its hard to tell.

Change-Id: I7b997666474ec324c5034e3660a7271b8423bca8
DocImpact:
UpgradeImpact:
Objectify association in neutronapi

This makes the neutronapi use the Instance object for the associate
path and updates the test to match.

Related to blueprint compute-manager-objects-juno

Change-Id: I045bfbd16e3b45107bd11e3874ce47280574930a
Merge "Objectify association in neutronapi"
Merge "Update migration defaults"