Clarified applicability of wsdl_location setting

Made the following changes:
* Edited the "VMwareVCDriver configuration options" section by removing
reference to wsdl_location option from code sample.
* Added note that this setting applies only to vSphere versions 5.0
and earlier. Note includes link to "vSphere 5.0 and earlier additional
set up" section below.
* Edited the "vSphere 5.0 and earlier additional set up" section with
text about the wsdl_location option specifically. Added link to the
"VMwareVCDriver configuration options" section above.

Change-Id: I90ffeda3528c98f4a19235798b07ed39f0dae407
backport: havana
Closes-Bug: #1273330
Merge "Clarified applicability of wsdl_location setting"