Improving onos-create-app script to print message when artifactId is not provided on command line.

This replaces the "onos-create-app: line 31: [: argument expected" error message.

Change-Id: I58e08f302edf2a5068adf993cdbc55e71b9578bf

@@ -28,7 +28,15 @@ mvn archetype:generate -DarchetypeGroupId=org.onosproject \
     -DarchetypeVersion=$ONOS_POM_VERSION $otherOptions "$@"
 
 # Patch the pom.xml file to make this an app.
-if [ $type = app -a -d $dir ]; then
+if [ $type = app ]; then
+    # We need to add a few lines to the pom.xml to make this an app
+    if [ -n "$dir" ] && [ -d $dir ]; then
         egrep -v "        (<!--|-->)" $dir/pom.xml > $dir/pom.app.xml
         mv $dir/pom.app.xml $dir/pom.xml
+    else
+        echo
+        echo "IMPORTANT:"
+        echo "To build the application, you need to uncomment the 'onos.app.name' and 'onos.app.origin' properties in the pom.xml"
+        echo
+    fi
 fi