Use a unique name for cell reservation

Change-Id: Ie1b6d5d7aed21010a7c005a2507ed7412f53f573
diff --git a/jjb/onos/onos-run-stc.sh b/jjb/onos/onos-run-stc.sh
index 150348f..130abcd 100644
--- a/jjb/onos/onos-run-stc.sh
+++ b/jjb/onos/onos-run-stc.sh
@@ -14,13 +14,13 @@
 
 # always free the cell when exiting
 function cleanup {
-  cell return
+  cell return jenkins-${ONOS_VERSION}
 }
 
 trap cleanup EXIT
 
 # grab a cell to run on
-cell borrow
+cell borrow 30 3+1 jenkins-${ONOS_VERSION}
 
 # build onos bits
 onos-buck build onos