Set the zone if specified in the SOAP request

https://bugzilla.redhat.com/show_bug.cgi?id=1135627

The required zone can be specified in the "parameters" being passed
to CreateAutomationRequest. The attribute name is called miq_zone
@gmcculloug 
If we want to allow nils coming from a soap caller, we would have to make sure we don't raise an ArgumentError when the :miq_zone is nil