Don't kill nova-bm-deploy-helper prematurally

This change ensure that 'nova-baremetal-deploy-helper' process is
not killed by stack.sh when USE_SCREEN=False

Change-Id: I84f6f3c3d09bf0cd0d4c5d94eb486a1f7d0b1d0f
diff --git a/stack.sh b/stack.sh
index 89a03b5..cf3baa2 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1222,7 +1222,7 @@
     fi
     # ensure callback daemon is running
     sudo pkill nova-baremetal-deploy-helper || true
-    screen_it baremetal "nova-baremetal-deploy-helper"
+    screen_it baremetal "cd ; nova-baremetal-deploy-helper"
 fi
 
 # Save some values we generated for later use