Add sleep after drivetrain update to wait salt completed all jobs

PROD-36385

Change-Id: I9b28e8a35abb666fe5180274e5c3136b4e8bfb1a
diff --git a/tcp_tests/requirements.txt b/tcp_tests/requirements.txt
index 462fa77..194b275 100644
--- a/tcp_tests/requirements.txt
+++ b/tcp_tests/requirements.txt
@@ -23,6 +23,8 @@
 python-jenkins
 cmd2<0.9
 PyYAML!=5.1
+polling==0.3.2
+
 
 # For Queens: https://github.com/openstack/requirements/blob/stable/queens/global-requirements.txt
 python-heatclient>=1.10.0