[miq_provision_virt_workflow.rb] Specify vm cols

This reduces the number of columns returned from the VMs table to
reduce what is returned and serialized from the DB.

Benchmark
---------

**Before**

|     ms | queries | query (ms) |   rows |
|   ---: |    ---: |       ---: |   ---: |
|  39488 |      33 |     2439.4 | 243133 |
|  38879 |      33 |     2438.2 | 243133 |
|  39256 |      33 |     2444.3 | 243133 |

**After**

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

app/models/miq_provision_virt_workflow.rb

@@ -339,6 +339,9 @@ def allowed_templates(options = {})
       end
     end
 
+    # Only select the colums we need
+    vms = vms.select(:id, :name, :guid, :uid_ems, :ems_id)
+
     allowed_templates_list = source_vm_rbac_filter(vms, condition, VM_OR_TEMPLATE_EXTRA_COLS).to_a
     @allowed_templates_filter = filter_id
     @allowed_templates_tag_filters = @values[:vm_tags]