Use latest version of python-openstackclient

Some options in openstack client like --or-show are available only
from 1.0.0. Adding this 'requirement' explictly as openstackclient
is not as part of requirements of other projects.

Change-Id: I96a98331ece15da869a3ea7af80d16fab2351329
diff --git a/stack.sh b/stack.sh
index cd1c200..375be28 100755
--- a/stack.sh
+++ b/stack.sh
@@ -780,7 +780,7 @@
     git_clone_by_name "python-openstackclient"
     setup_dev_lib "python-openstackclient"
 else
-    pip_install python-openstackclient
+    pip_install 'python-openstackclient>=1.0.0'
 fi