Make nova-network use FixedIP object for disassociations

This makes nova-network mananger use the FixedIP object for
disassociating IPs.

Related to blueprint nova-network-objects

Change-Id: Ia0a38bbd31cc22095893bff89bcaa402a9bc2722
Replace oslo.sphinx with oslosphinx

oslosphinx is now available as a replacement for oslo.sphinx that
won't conflict with oslo.config in virtual envs.

Change-Id: I7c116f816af895261e76af385ee3e9288e6fa70f
Closes-Bug: #1277168
Don't allow compute_node free_disk_gb to be None

As part of commit 5668870, we now explicitly guard against the case
free_disk_gb is None or unset. However, this should never happen
since resource tracker always sets it and guarding against this case
isn't actually needed to fix the bug in question.

Also, simplify the code a little to make the intent more clear. We
assume that free_disk_gb is always set, but we want to use
disk_available_least where the driver has set it. The case where
disk_available_least is less than free_disk_gb is the exceptional
case we want to guard against.

Change-Id: I3973eab6b4ca016df546de8b57245fc0d0f03a80
Convert unrescue_instance to objects

Related to blueprint icehouse-objects.
Related to blueprint compute-manager-objects.

Change-Id: Id1311064354ee055a3557ce6aafca148c76524ec
Merge "Don't allow compute_node free_disk_gb to be None"
Merge "Convert unrescue_instance to objects"
Merge "Replace oslo.sphinx with oslosphinx"
Merge "Make nova-network use FixedIP object for disassociations"