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
Merge "Replace oslo.sphinx with oslosphinx"
Merge "Make nova-network use FixedIP object for disassociations"