fix: contributing build

* Always `npm install` samples/package.json before running sample tests
* Copy, rather than symlink, in `test.samples.auth`

Partially fixes googleapis#2377.

package.json

@@ -21,7 +21,7 @@
     "docs": "node build/src/generator/docs",
     "presystem-test": "npm run compile",
     "system-test": "mocha build/system-test",
-    "samples-test": "cd samples && npm link ../ && pwd && npm test",
+    "samples-test": "cd samples && npm install && npm link ../ && pwd && npm test",
     "lint": "gts check",
     "compile": "tsc -p .",
     "build-tools": "tsc -p tsconfig.tools.json",

samples/test/test.samples.auth.js

@@ -41,7 +41,8 @@ describe('Auth samples', () => {
     const realPath = path.resolve('jwt.keys.json');
     const exists = fs.existsSync(realPath);
     if (!exists) {
-      fs.symlinkSync(fakePath, realPath);
+      const contents = fs.readFileSync(fakePath);
+      fs.writeFileSync(realPath, contents);
     }
     const data = await samples.jwt.runSample();
     assert(data);