Increasing capacity of cinder-volume loop device

Extending of cinder-volume loop-back device up to 20GB due to
the fact that 10GB is not enough for Tempest Stepler tests.

Change-Id: Ieb71940c9a7e8c01d0a78eb879a53219ba6fd6ce
Related-PROD: PROD-14724
diff --git a/classes/cluster/virtual-mcp11-aio/init.yml b/classes/cluster/virtual-mcp11-aio/init.yml
index b3fcc39..9768e1f 100755
--- a/classes/cluster/virtual-mcp11-aio/init.yml
+++ b/classes/cluster/virtual-mcp11-aio/init.yml
@@ -31,7 +31,7 @@
     mysql_admin_password: workshop
     rabbitmq_secret_key: workshop
     rabbitmq_admin_password: workshop
-    loopback_device_size: 10
+    loopback_device_size: 20
     salt_master_host: 192.168.10.90
     salt_master_base_environment: prd
     salt_minion_ca_host: ${linux:network:fqdn}