Add no-babelrc option in babel-node (#5621)

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| Q                        | A <!--(yes/no) -->
| ------------------------ | ---
| Patch: Bug Fix?          | 
| Major: Breaking Change?  | 
| Minor: New Feature?      | y
| Deprecations?            | 
| Spec Compliancy?         | 
| Tests Added/Pass?        | y/y
| Fixed Tickets            | #5616
| License                  | MIT
| Doc PR                   | <!-- if yes, add `[skip ci]` to your commit message to skip CI builds -->
| Dependency Changes       | 

<!-- Describe your changes below in as much detail as possible -->

Once merged I will make the corresponding documentation changes on the website (in a 7 branch)

packages/babel-cli/test/index.js

@@ -36,7 +36,9 @@ const readDir = function(loc, filter) {
 
 const saveInFiles = function(files) {
   // Place an empty .babelrc in each test so tests won't unexpectedly get to repo-level config.
-  outputFileSync(".babelrc", "{}");
+  if (!fs.existsSync(".babelrc")) {
+    outputFileSync(".babelrc", "{}");
+  }
 
   Object.keys(files).forEach(function(filename) {
     const content = files[filename];