[miq_provision_virt_workflow.rb] Avoid respond_to?

respond_to? calls in mass are slow since they require some object
introspection, where doing a simple `nil` check is much quicker.

By including just the `cloud_tenant_id` in the SELECT clause, it allows
for the swapping of `respond_to?` with an `nil` check, with the
functionality that existed preserved.

Benchmark
---------

**Before**

|     ms | queries | query (ms) |   rows |
|   ---: |    ---: |       ---: |   ---: |
|  28440 |      33 |     1929.5 | 243133 |
|  28491 |      33 |     1933.6 | 243133 |
|  28858 |      33 |     2631.9 | 243133 |

**After**

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

app/models/miq_provision_virt_workflow.rb

@@ -340,7 +340,7 @@ def allowed_templates(options = {})
     end
 
     # Only select the colums we need
-    vms = vms.select(:id, :name, :guid, :uid_ems, :ems_id)
+    vms = vms.select(:id, :name, :guid, :uid_ems, :ems_id, :cloud_tenant_id)
 
     allowed_templates_list = source_vm_rbac_filter(vms, condition, VM_OR_TEMPLATE_EXTRA_COLS).to_a
     @allowed_templates_filter = filter_id
@@ -1046,7 +1046,7 @@ def create_hash_struct_from_vm_or_template(vm_or_template, options)
                  :allocated_disk_storage => vm_or_template.allocated_disk_storage,
                  :v_total_snapshots      => vm_or_template.v_total_snapshots,
                  :evm_object_class       => :Vm}
-    data_hash[:cloud_tenant] = vm_or_template.cloud_tenant if vm_or_template.respond_to?(:cloud_tenant)
+    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)
     end