Add sleep after drivetrain update to wait salt completed all jobs

PROD-36385

Change-Id: I9b28e8a35abb666fe5180274e5c3136b4e8bfb1a
diff --git a/tcp_tests/tests/system/test_mcp_update.py b/tcp_tests/tests/system/test_mcp_update.py
index c1456be..45e3cdd 100644
--- a/tcp_tests/tests/system/test_mcp_update.py
+++ b/tcp_tests/tests/system/test_mcp_update.py
@@ -188,6 +188,7 @@
             2. Run job git-mirror-downstream-mk-pipelines
             3. Run job git-mirror-downstream-pipeline-library
             4. If jobs are passed then start 'Deploy - upgrade MCP Drivetrain'
+            5. Wait till salt-master completes all async jobs
 
         Duration: ~70 min
         """
@@ -248,6 +249,9 @@
             build_timeout=4 * 60 * 60)
 
         assert job_result == 'SUCCESS', job_description
+        # ############### Wait till salt-master completes all async jobs #####
+        show_step(5)
+        salt.wait_jobs_completed(timeout=20*60)
 
     @pytest.mark.grab_versions
     @pytest.mark.parametrize("_", [settings.ENV_NAME])