correctly set iface-id in vmware driver

bug 1183452

Commit 70c659059b8fbef811ce79700aecb01c60242ebd updated the vmware
driver to use the new vif model, but was incorrect in how it tried to
grab the iface-id and set it in the vmx file spec.  This patch fixes
that issue and adds a check for this in the existing unit tests.

Change-Id: I756539871d1844a828f9a0a295fc9fa3e59610f7
(cherry picked from commit c028e54f6be75d1cd335550cf5291ddf94f973e3)
Merge "correctly set iface-id in vmware driver" into stable/grizzly