Pin python-openstackclient

Change-Id: I68189ba4772d7bad955f2ec4f1bd1baa6c5a62c4
diff --git a/tcp_tests/requirements.txt b/tcp_tests/requirements.txt
index 759a449..e9c2917 100644
--- a/tcp_tests/requirements.txt
+++ b/tcp_tests/requirements.txt
@@ -27,5 +27,5 @@
 # For Queens: https://github.com/openstack/requirements/blob/stable/queens/global-requirements.txt
 python-heatclient>=1.10.0
 python-glanceclient>=2.8.0
-python-openstackclient>=3.12.0
+python-openstackclient==3.18.0
 keystoneauth1>=3.3.0