Make floating_ips module use FloatingIP for all get queries

This makes the network.floating_ips module use the FloatingIP
object for all get_* queries instead of direct database access.

Related to blueprint nova-network-objects

Change-Id: I862f2f3abc078b477bea6bf86d0d622c4e78881f
Merge "Make floating_ips module use FloatingIP for all get queries"