Add tools/make_cert.sh

This allows use of either the DevStack CA or creating another CA
independent of stack.sh.

Change-Id: I055679b5fd06e830c8e6d7d7331c52dd8782d0b6
diff --git a/stack.sh b/stack.sh
index 9f734b9..d43e81c 100755
--- a/stack.sh
+++ b/stack.sh
@@ -838,6 +838,7 @@
 if is_service_enabled tls-proxy; then
     configure_CA
     init_CA
+    init_cert
     # Add name to /etc/hosts
     # don't be naive and add to existing line!
 fi