Avoid duplicate host load in allowed_hosts_obj

MiqRequestWorkflow#allowed_hosts_obj originally would collect the known
host ids from the ems tree it has already built up and combine those
with any hosts associated to the storage it had, and then do a query
against the `src[:ems]`'s hosts and select only the ones that match the
original set of host ids.  From there, it would take that list of host
objects, throw it through, Rbac which would also make another query to
find the hosts that match that list AND filter it based on the user
(throwing out the previously instantiated hosts that were used as the
intermediate list from `src[:ems]`).

This change simply avoids creating that intermediate list by replacing
the `.find_all` with a `.where`, meaning we pass a scoped query to Rbac
that hasn't been executed until it has the user filter applied to it.

Metrics
-------

When selecting the `"Lifecycle" -> "Publish this VM to a Template"`
button:

**Before**

|    ms | queries | query (ms) |  rows |
|  ---: |    ---: |       ---: |  ---: |
| 18613 |    2062 |     1463.7 | 70017 |
| 17695 |    2062 |     1475.5 | 70017 |
| 17774 |    2062 |     1578.4 | 70017 |

**After**

|    ms | queries | query (ms) |  rows |
|  ---: |    ---: |       ---: |  ---: |
| 18553 |    2061 |     1560.7 | 61866 |
| 17385 |    2061 |     1564.6 | 61866 |
| 17468 |    2061 |     1437.5 | 61866 |

app/models/miq_request_workflow.rb

@@ -1041,7 +1041,7 @@ def allowed_hosts_obj(options = {})
     return [] if hosts_ids.blank?
 
     # Remove any hosts that are no longer in the list
-    all_hosts = load_ar_obj(src[:ems]).hosts.find_all { |h| hosts_ids.include?(h.id) }
+    all_hosts = load_ar_obj(src[:ems]).hosts.where(:id => hosts_ids)
     allowed_hosts_obj_cache = process_filter(:host_filter, Host, all_hosts)
     _log.info("allowed_hosts_obj returned [#{allowed_hosts_obj_cache.length}] objects in [#{Time.now - st}] seconds")
     rails_logger('allowed_hosts_obj', 1)