NSX: add nsx switch lookup to dhcp and metadata operations

The operations in questions were still using the neutron network
uuid as the nsx switch uuid, but this is no longer valid.

Close-bug: #1312439

Change-Id: I0f4bf02bb176c5c3914c7dd7e8249121af1b5a79
Merge "NSX: add nsx switch lookup to dhcp and metadata operations"