NSX: pass the right argument during metadata setup

The NSX cluster was erroneously passed instead of context.
This patch addressed that and tweaks UT to verify the right
parameter is passed instead.

Change-Id: Ife660b3a23705342043d121c7dcecad43e22abc1
Closes-bug: #1315538
(cherry picked from commit a3a8a86d7bccb824725d91735bd032237786f5aa)