Fix VM Provision datastore location class

When building the `VirtualMachineRelocateSpec` the `datastore` property
is a `ManagedObjectReference` to a `Datastore`.  We were setting the
value to a simple `String` rather than a `VimString` with the proper
`xsiType`/`vimType`.

This would have broken when we moved from having VimString in ems_ref as
a serialized yaml column and added ems_ref_obj.

app/models/manageiq/providers/vmware/infra_manager/provision/cloning.rb

@@ -168,7 +168,7 @@ def clone_vm(vim_clone_options)
 
   def datastore_ems_ref(clone_opts)
     datastore = Storage.find_by(:id => clone_opts[:datastore].id)
-    datastore.try(:ems_ref)
+    datastore.try(:ems_ref_obj)
   end
 
   def get_selected_snapshot

spec/models/manageiq/providers/vmware/infra_manager/provision_spec.rb

@@ -298,7 +298,7 @@
         before(:each) do
           Array.new(2) do |i|
             ds_mor = "datastore-#{i}"
-            storage = FactoryBot.create(:storage_nfs, :ems_ref => ds_mor, :ems_ref_type => "Datastore")
+            storage = FactoryBot.create(:storage_vmware, :ems_ref => ds_mor, :ems_ref_type => "Datastore")
 
             cluster_mor = "cluster-#{i}"
             cluster     = FactoryBot.create(:ems_cluster, :ems_ref => cluster_mor)