OS-534 Fix IP allocation for Infoblox IPAM

Port creation failed for Infoblox IPAM with KeyError.

Change-Id: I6440ece398bbe8742a65aa1ce69032b266126c90
Merge pull request #6 from roman-verchikov/bp/infoblox-plugin-neutron

OS-534 Fix IP allocation for Infoblox IPAM