Update neutronv2/api.py to work with nova icehouse

In nova icehouse a couple of method signature changed,
this commit fix them

Change-Id: I72600d98a1d81683dd8b99ddfe94356716f344ad
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>
Merge pull request #22 from rodis/stable/icehouse

Update neutronv2/api.py to work with nova icehouse