Handle 405 error codes correctly in NVP plugin

When NVP returns a 405 error code no exception is
raised, causing the plugin to assume that everything
went well when it didn't.

Fixes bug #1243411

Change-Id: If70db05b8c6950bfa88a36c4f0c20ee80419d31d
Merge "Handle 405 error codes correctly in NVP plugin"