Dell EMC SC: Add use_multipath_for_image_xfer

This change implements the documented best practice to use multipath
with a Cinder deployment by setting a Cinder configuration setting
to ensure that multipath is appropriately used by the Dell EMC
SC iSCSI driver.
This backport modified the default value to ::os_service_default
in order to not introduce behavior changes.

Change-Id: Ie50e29bd96471110a3738e3fcccfb8af37cd31be
(cherry picked from commit 72035c5e3c)

manifests/backend/dellsc_iscsi.pp

@@ -74,6 +74,10 @@
 #   with volume_backend_name=$volume_backend_name key/value.
 #   Defaults to false.
 #
+# [*use_multipath_for_image_xfer*]
+#   (Optional) Enables multipath configuration.
+#   Defaults to to $::os_service_default
+#
 define cinder::backend::dellsc_iscsi (
   $san_ip,
   $san_login,
@@ -92,6 +96,7 @@ define cinder::backend::dellsc_iscsi (
   $secondary_san_password       = $::os_service_default,
   $secondary_sc_api_port        = $::os_service_default,
   $manage_volume_type           = false,
+  $use_multipath_for_image_xfer = $::os_service_default,
   $extra_options          = {},
 ) {
 
@@ -126,6 +131,7 @@ default of \"vol\" and will be changed to the upstream OpenStack default in N-re
     "${name}/secondary_san_login":          value => $secondary_san_login;
     "${name}/secondary_san_password":       value => $secondary_san_password, secret => true;
     "${name}/secondary_sc_api_port":        value => $secondary_sc_api_port;
+    "${name}/use_multipath_for_image_xfer": value => $use_multipath_for_image_xfer;
   }
 
   if $manage_volume_type {

releasenotes/notes/dellsc-driver-a7cd300a24a64b01.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - Add the ability to configure the multipath setting for
+    the Dell EMC SC ISCSI driver.

spec/defines/cinder_backend_dellsc_iscsi_spec.rb

@@ -28,6 +28,7 @@ describe 'cinder::backend::dellsc_iscsi' do
       :secondary_san_login          => '<SERVICE DEFAULT>',
       :secondary_san_password       => '<SERVICE DEFAULT>',
       :secondary_sc_api_port        => '<SERVICE DEFAULT>',
+      :use_multipath_for_image_xfer => '<SERVICE DEFAULT>',
     }
   end