Remove relative imports from NVP plugin

The majority of relative imports in the nvp plugin will be fixed in
blueprint nvp-api-client-loadbalance-request. This patch removes the
rest of them in and moves the vim tabstop line to the top of the
header file to be consistent with the rest of the files in quantum.
Fixes bug 1091596

Change-Id: I6c8299ca73ae5df75c87f302680908f863f81f02