vcsim: fix fault detail encoding
vcsim: fix fault detail encoding

The Detail.Fault field was coded with the field name "Fault",
when it should be "${TypeOfFault}Fault".

This wasn't an issue for Go clients, as the soap.Fault is tagged with
xml:,any - so the name is ignored and only the xsi type is needed.

Fixes #1261

bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi,vmware/govmomi