[miq_provision_virt_workflow.rb] Use VmOrTemplate#platform

Very large performance improvement from this patch on large collections
of templates since it avoids preloading all together, reducing the
number of iterations over the VM collection, and the number of support
objects needing to be introduced (that would later need to be garbage
collected.

Benchmark
---------

**Before**

|     ms | queries | query (ms) |   rows |
|   ---: |    ---: |       ---: |   ---: |
|  27107 |      33 |     1958.5 | 243133 |
|  26803 |      33 |     1944.2 | 243133 |
|  27642 |      33 |     1965.5 | 243133 |

**After**

|     ms | queries | query (ms) |   rows |
|   ---: |    ---: |       ---: |   ---: |
|  14344 |      33 |     1759.6 | 243133 |
|  14631 |      33 |     1729.0 | 243133 |
|  13405 |      33 |     1752.3 | 243133 |

app/models/miq_provision_virt_workflow.rb

@@ -298,7 +298,13 @@ def tag_symbol
     :vm_tags
   end
 
-  VM_OR_TEMPLATE_EXTRA_COLS = %i(mem_cpu cpu_total_cores v_total_snapshots allocated_disk_storage).freeze
+  VM_OR_TEMPLATE_EXTRA_COLS = %i(
+    platform
+    mem_cpu
+    cpu_total_cores
+    v_total_snapshots
+    allocated_disk_storage
+  ).freeze
   def allowed_templates(options = {})
     # Return pre-selected VM if we are called for cloning
     if [:clone_to_vm, :clone_to_template].include?(request_type)
@@ -355,7 +361,6 @@ def allowed_templates(options = {})
       end
     end
 
-    MiqPreloader.preload(allowed_templates_list, %i(operating_system))
     @_ems_allowed_templates_cache = {}
     @allowed_templates_cache = allowed_templates_list.collect do |template|
       create_hash_struct_from_vm_or_template(template, options)
@@ -1055,7 +1060,7 @@ def create_hash_struct_from_vm_or_template(vm_or_template, options)
                  :evm_object_class       => :Vm}
     data_hash[:cloud_tenant] = vm_or_template.cloud_tenant if vm_or_template.cloud_tenant_id
     if vm_or_template.operating_system
-      data_hash[:operating_system] = MiqHashStruct.new(:product_name => vm_or_template.operating_system.product_name)
+      data_hash[:operating_system] = MiqHashStruct.new(:product_name => vm_or_template.operating_system_product_name)
     end
     if options[:include_datacenter] == true
       data_hash[:datacenter_name] = vm_or_template.owning_blue_folder.try(:parent_datacenter).try(:name)