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
:+1: @gmcculloug ... @matthewd's version is cleaner than both versions and provides what you want by using Hash#fetch's default value when the key isn't found.