Update the "onos-service" command:

 - add a mechanism to print the usage.
 - If the target is "--cell", the service command is executed on each
   node in the current ONOS cell.

Usage:     onos-service <TARGET> [COMMAND]
           onos-service [-h | --help]
Options:
    TARGET          The target of the command
    COMMAND         The command to execute. Default value is 'status'
    [-h | --help]   Print this help

TARGET:  <hostname | --cell>
      hostname        Execute on the specified host name
        --cell        Execute on the current ONOS cell

COMMAND: [start|stop|restart|status]

@@ -6,4 +6,39 @@
 [ ! -d "$ONOS_ROOT" ] && echo "ONOS_ROOT is not defined" >&2 && exit 1
 . $ONOS_ROOT/tools/build/envDefaults
 
-ssh $ONOS_USER@${1:-$OCI} "sudo service onos ${2:-status}"
+function print_usage {
+    command_name=`basename $0`
+    echo "Remotely administer the ONOS service on a single node or the current ONOS cell."
+    echo
+    echo "Usage:     $command_name <TARGET> [COMMAND]"
+    echo "           $command_name [-h | --help]"
+    echo "Options:"
+    echo "    TARGET          The target of the command"
+    echo "    COMMAND         The command to execute. Default value is 'status'"
+    echo "    [-h | --help]   Print this help"
+    echo ""
+    echo "TARGET:  <hostname | --cell>"
+    echo "      hostname        Execute on the specified host name"
+    echo "        --cell        Execute on the current ONOS cell"
+    echo ""
+    echo "COMMAND: [start|stop|restart|status]"
+    echo ""
+}
+
+# Print usage
+if [ "${1}" = "-h" -o "${1}" = "--help" ]; then
+    print_usage
+    exit 0
+fi
+
+# Select the target
+if [ "${1}" = "--cell" ]; then
+    nodes=$(env | sort | egrep "OC[0-9]+" | cut -d= -f2)
+else
+    nodes=${1:-$OCI}
+fi
+
+# Execute the remote commands
+for node in $nodes; do
+    ssh $ONOS_USER@${node} "sudo service onos ${2:-status}"
+done