improve tests for nodeDir

Adds new resources (loose files, non NR pkgs, NR modules, NR Plugins)
Adds new tests
#getNodeFiles - new tests below
  √ Finds nodes and icons only in nodesDir with files, icons and valid node-red packages
  √ Should not find node-red node in nodesDir with files, icons and valid node-red packages
  √ Should not find node-red node in nodesDir when regular package and valid node-red packages
#getModuleFiles - new tests below
  √ gets a nodes module files
  √ Finds only 1 node-red node in nodesDir amongst legacy nodes and regular nodes
  √ Finds a node-red node in nodesDir with a sub dir containing valid node-red package
  √ Finds 2 node-red node and 1 plugin in nodesDir (in root of dir)
  √ Finds 2 node-red node and 1 plugin in nodesDir pointing to a node_modules dir

test/unit/@node-red/registry/lib/resources/nodesDir1/node-red-node-testnode/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "node-red-node-testnode",
+  "version": "1.0.0",
+  "description": "A node-red node that does nothing other than exist",
+  "main": "main.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [
+    "node-red"
+  ],
+  "node-red": {
+    "nodes": {
+      "testnode": "index.js"
+    }
+  },
+  "author": "@testyMcTersterson",
+  "license": "MIT"
+}