Add workaround for sphinx_proxy_password_generated

The update-drivetrain proccess fails without sphinx_proxy_password_generated
Causes error:
[WARNING] Reference '${_param:cluster_node03_address}' undefined
-> prx02.released-heat-cicd-pike-dvr-sl.local
   Cannot resolve ${_param:sphinx_proxy_password_generated}, at _param:nginx_proxy_sphinx_password, in yaml_fs:///srv/salt/reclass/classes/system/sphinx/server/doc/reclass.yml

Change-Id: I7b3eb1ef78a7bb5cbd8dd615a42ca8e8ae32a91c
Related-Prod:#PROD-34406
diff --git a/tcp_tests/tests/system/test_mcp_update.py b/tcp_tests/tests/system/test_mcp_update.py
index ca68a71..4224278 100644
--- a/tcp_tests/tests/system/test_mcp_update.py
+++ b/tcp_tests/tests/system/test_mcp_update.py
@@ -95,6 +95,16 @@
     salt_actions.enforce_state("I@jenkins:client", "jenkins.client")
 
 
+@pytest.fixture
+def wa_for_sphinx_prod34406(reclass_actions, salt_actions):
+    reclass_actions.add_key(
+        "parameters._param.sphinx_proxy_password_generated",
+        "a"*32,
+        "cluster/*/infra/secrets.yml")
+    salt_actions.run_state("I@nginx:server",
+                           "saltutil.refresh_pillar")
+
+
 @pytest.fixture(scope='class')
 def enable_openstack_update(reclass_actions, salt_actions):
     param = "parameters._param.openstack_upgrade_enabled"
@@ -109,7 +119,8 @@
     salt_actions.run_state("*", "saltutil.refresh_pillar")
 
 
-@pytest.mark.usefixtures("switch_to_proposed_pipelines")
+@pytest.mark.usefixtures("switch_to_proposed_pipelines",
+                         "wa_for_sphinx_prod34406")
 class TestUpdateMcpCluster(object):
     """
     Following the steps in