Update Global-JJB to master

This is a temporary update until a new release of Global-JJB comes out.

Updating Global-JJB to a commit on master past 0.19.2 which allows
jjb jobs to run on the same builder without tripping over each other.

The related Gerrit change for the current tip of master can be seen
here: https://gerrit.linuxfoundation.org/infra/#/c/10717/

Change-Id: I4205fc74d8af805ac29ac93d4c5b033c145a00b9
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>

diff --git a/jjb/global-jjb b/jjb/global-jjb
index 1493b95..9b24045 160000 (submodule)
--- a/jjb/global-jjb
+++ b/jjb/global-jjb
@@ -1 +1 @@
-Subproject commit 1493b95e0d80860a9d8aef83e22ee49d5988ad96
+Subproject commit 9b240453b91f3c4b0844ea1c593721a1c421caa2