Fix use of invalid variable in tgt exists check

I added a check for tgt already exists here:
https://review.openstack.org/#/c/138173/

But, that was wrong, the err value is never going to be
set because of the exception.  This should have inspected
the exception object and checked against it.

So this patch makes it do what it was supposed to do.

Change-Id: I8c184bf1684c8592a36f749cdcb5493f6b65e52b
FibreChannel drivers for NetApp Data ONTAP storage controllers

This patch adds FibreChannel support to NetApp's Cinder drivers
for Data ONTAP (7-mode and Cluster-mode).  The drivers make full
use of Cinder's FibreChannel zone manager.

Implements blueprint add-fibre-channel-support-to-netapp-drivers
Change-Id: Ifbda275e4a60dda144a169ef00a4ea5e548dfa03
Merge "FibreChannel drivers for NetApp Data ONTAP storage controllers"
Merge "Fix use of invalid variable in tgt exists check"