Switch heat-engine workers to use os_workers_heat_engine

Previously the default value for the heat-engine workers setting was set
to $::os_service_default. We usually use our specific facts for the
worker settings so this change switches it to use the
$::os_worker_heat_engine fact.

Change-Id: I6a8d745b76afca1b1958816fa10a3f1dd30face6
Related-Bug: #1763671

manifests/engine.pp

@@ -103,7 +103,7 @@
 #
 # [*num_engine_workers*]
 #   (Optional) The number of workers to spawn.
-#   Defaults to $::os_service_default.
+#   Defaults to $::os_workers_heat_engine
 #
 # [*convergence_engine*]
 #   (Optional) Enables engine with convergence architecture.
@@ -147,7 +147,7 @@ class heat::engine (
   $instance_connection_is_secure                   = $::os_service_default,
   $instance_connection_https_validate_certificates = $::os_service_default,
   $max_resources_per_stack                         = $::os_service_default,
-  $num_engine_workers                              = $::os_service_default,
+  $num_engine_workers                              = $::os_workers_heat_engine,
   $convergence_engine                              = $::os_service_default,
   $reauthentication_auth_method                    = $::os_service_default,
   $environment_dir                                 = $::os_service_default,

releasenotes/notes/heat-engine-workers-8ef3960a29c21a57.yaml

@@ -0,0 +1,11 @@
+---
+fixes:
+  - |
+    Previously the number of heat engine workers was set to $::os_service_default
+    which would use the default from python. Usually this means it will use
+    the number of processors in the system. We have found that this is not an
+    ideal default for large number of cpu systems. We have a provided fact
+    specific to heat engine named $::os_workers_heat_engine. We have changed
+    the default value for the heat engine works to use this fact. This
+    fact will cap the value at 24 but usually is the larger of
+    (number of procs / 2) or 4.

spec/classes/heat_engine_spec.rb

@@ -139,7 +139,7 @@ describe 'heat::engine' do
   }).each do |os,facts|
     context "on #{os}" do
       let (:facts) do
-        facts.merge!(OSDefaults.get_facts())
+        facts.merge!(OSDefaults.get_facts({:os_workers_heat_engine => 2}))
       end
 
       let :platform_params do