Adding groupId to archetypes/pom.xml

As a top-level pom on which mvn versions:set is called, it needs to have a groupId
to avoid an NPE when mvn runs.

Change-Id: Id85889af117abbcf7a5f9e6e0f87bd9f7077d1ac

@@ -26,6 +26,7 @@
         <relativePath>../../build/pom.xml</relativePath>
     </parent>
 
+    <groupId>org.onosproject</groupId>
     <artifactId>onos-archetypes</artifactId>
     <version>1.2.0-SNAPSHOT</version>
     <packaging>pom</packaging>