[MDEP-842] Use skip field in :list-classes

Author: pzygielo

src/main/java/org/apache/maven/plugins/dependency/ListClassesMojo.java

@@ -149,6 +149,10 @@ public class ListClassesMojo extends AbstractMojo {
 
     @Override
     public void execute() throws MojoExecutionException, MojoFailureException {
+        if (skip) {
+            getLog().info("Skipping plugin execution");
+            return;
+        }
         ProjectBuildingRequest buildingRequest = makeBuildingRequest();
 
         try {