Decrease salt master workers

This improves speed of tests in more than 2 times and
allows to avoid scenario test instability.

Change-Id: Ib6a4b8c48f52361606d7447f553d042f66f5f639
Related-Prod: https://mirantis.jira.com/browse/PROD-16465
(cherry picked from commit ffdc075dcd0dd36cc7dc31b301e147310912ff76)
diff --git a/classes/cluster/virtual-mcp11-aio/infra/config.yml b/classes/cluster/virtual-mcp11-aio/infra/config.yml
index c59029b..c96f4b0 100644
--- a/classes/cluster/virtual-mcp11-aio/infra/config.yml
+++ b/classes/cluster/virtual-mcp11-aio/infra/config.yml
@@ -8,3 +8,6 @@
       name: cfg01
       domain: ${_param:cluster_domain}
       purge_repos: ${_param:linux_system_purge_repos}
+  salt:
+    master:
+      worker_threads: 5