VMware: iscsi target discovery fails while attaching volumes

VMware Drivers are unable to discover iscsi targets because
the api calls fail to specify the iscsi server location
(referred in the code as target portal) to retrieve targets.
This is critical for the attach_volume feature to work with
iscsi supported cinder drivers.

Closes-Bug: #1235112

Change-Id: I60c06ae651bb2eb6d466a5ca61a09f289c21d1a3
Merge "VMware: iscsi target discovery fails while attaching volumes"