Update client-env to use openstackclient commands

Updated the only instance of a keystoneclient command, to
check if the identity service is enabled.

Change-Id: If86f71c1610a79690d6c6a8eb423b6fa234372bb
diff --git a/exercises/client-env.sh b/exercises/client-env.sh
index d955e4d..4e8259c 100755
--- a/exercises/client-env.sh
+++ b/exercises/client-env.sh
@@ -64,7 +64,7 @@
         STATUS_KEYSTONE="Skipped"
     else
         echo -e "\nTest Keystone"
-        if keystone catalog --service identity; then
+        if openstack endpoint show identity; then
             STATUS_KEYSTONE="Succeeded"
         else
             STATUS_KEYSTONE="Failed"