Optionally set device_driver to $::os_service_default

This commit will give users to optionally set device_driver value in lbaas_agent.ini to $::os_service_default

Change-Id: I1a9d8094816c684bfb769617dce895f122323fb9

manifests/agents/lbaas.pp

@@ -64,6 +64,7 @@ class neutron::agents::lbaas (
         ensure_packages([$::neutron::params::haproxy_package])
       }
     }
+    $::os_service_default: {}
     default: {
       fail("Unsupported device_driver ${device_driver}")
     }

releasenotes/notes/option-to-set-device-driver-to-os-service-default-a5820845f828296c.yaml

@@ -0,0 +1,3 @@
+---
+features:
+  - Optionally users can set device_driver value in lbaas_agent.ini to $::os_service_default

spec/classes/neutron_agents_lbaas_spec.rb

@@ -90,6 +90,15 @@ describe 'neutron::agents::lbaas' do
         is_expected.to contain_neutron_lbaas_agent_config('DEFAULT/ovs_use_veth').with_value(false);
       end
     end
+
+    context 'with device_driver as $::os_service_default' do
+      before :each do
+        params.merge!(:device_driver => '<SERVICE DEFAULT>')
+      end
+      it 'should have devcie_driver set to $::os_service_default' do
+        is_expected.to contain_neutron_lbaas_agent_config('DEFAULT/device_driver').with_value('<SERVICE DEFAULT>');
+      end
+    end
   end
 
   shared_examples_for 'haproxy lbaas_driver' do