Make allow_{resize|migrate}_to_same_host configurable

In preparation for supporting 2 node devstack jobs, where the first node
is an all in one and the second is a compute node. Make nova config
options allow_resize_to_same_host and allow_migrate_to_same_host
configurable so we can turn them off when we have two compute nodes.

Change-Id: If6989200b56c4597d6e8506d0dda2cc75d0881f1
Merge "Make allow_{resize|migrate}_to_same_host configurable"