Warn users against the dangers of using Windows Explorer's zip action.

Using the Windows Explorer method of creating zip actions results in an incorrect zip structure. OW requires that package.json be found at the root of the zip, while the Explorer action insists on putting everything inside a top-level folder inside the zip.

Return an explicit error when package.json is not found at the root of a zipped action.

tests/src/actionContainers/NodeJsActionContainerTests.scala

@@ -444,7 +444,7 @@ class NodeJsActionContainerTests extends BasicActionRunnerTests with WskActorSys
         checkStreams(out, err, {
             case (o, e) =>
                 (o + e).toLowerCase should include("error")
-                (o + e).toLowerCase should include("module_not_found")
+                (o + e).toLowerCase should include("package.json must be located at the root of a zipped action")
         })
     }