Save rc from stack.sh in run-devstack role

Avoid overriding the failure state of stack.sh by the trailing echo
command.

Change-Id: I74820709edc98f67ff1a0c620ce5db3a3571b7f5
diff --git a/roles/run-devstack/tasks/main.yaml b/roles/run-devstack/tasks/main.yaml
index 1ff8295..f58b31d 100644
--- a/roles/run-devstack/tasks/main.yaml
+++ b/roles/run-devstack/tasks/main.yaml
@@ -2,7 +2,9 @@
   shell:
     cmd: |
       ./stack.sh 2>&1
+      rc=$?
       echo "*** FINISHED ***"
+      exit $rc
   args:
     chdir: "{{devstack_base_dir}}/devstack"
   become: true