NSX: port status must reflect fabric, not link status

This patch ensures the status attribute for the port resource is
semantically consistent with the reference plugin when using the
NSX plugin.

Change-Id: Ifb9c7664da926d3e6d5c6ec7c0e375b53a97582a
Closes-Bug: 1285426
Merge "NSX: port status must reflect fabric, not link status"