fix broken WSDL logic

vSphere driver incorrectly assumes that a WSDL is locally required.
A local WSDL is only needed as a work-around for certain situations.

Fixes bug 1171215

cherry picked from commit cf3cc74fcb65de3c59f98db001267e05ae405186

Change-Id: I1cc81d96e263ad586b903a74dc9d5c602d475dc9