Added "drivers" to cells that defined ONOS_APPS.

Change-Id: I8e7cbea037ea09504662fb17ef328b547d21050a
diff --git a/tools/test/cells/single b/tools/test/cells/single
index 19485a9..dd03e49 100644
--- a/tools/test/cells/single
+++ b/tools/test/cells/single
@@ -4,4 +4,4 @@
 export OC1="192.168.56.101"
 export OCN="192.168.56.103"
 
-export ONOS_APPS="openflow,fwd,proxyarp,mobility"
+export ONOS_APPS="drivers,openflow,fwd,proxyarp,mobility"