Suppress superfluous error message when pushing to a cell the first time.

If remote bits aren't found, it used to print:
  cksum: /tmp/onos-1.1.0.jono.tar.gz: No such file or directory

which may give the impression the install failed.

Fixes ONOS-704.

Change-Id: Ic03f3e546abad1e4dcfb69f61b7766be63c016ef

@@ -10,7 +10,7 @@ node=${1:-$OCI}
 remote=$ONOS_USER@$node
 
 locHash=$(cksum $ONOS_TAR | cut -d' ' -f1,2)
-remHash=$(ssh $remote cksum $ONOS_TAR | cut -d' ' -f1,2)
+remHash=$(ssh $remote cksum $ONOS_TAR 2>/dev/null | cut -d' ' -f1,2)
 
 if [ "$locHash" = "$remHash" ]; then
     echo "ONOS bits $ONOS_TAR already up-to-date on $node..."