test: fix flaky fs-watch tests

`test-fs-watch-recursive` and `test-fs-watch` were both watching the
same folder: `tmp/testsubdir` so running them sequentially on `OS X`
could make `test-fs-watch` to fail due to events generated in the other
test. Make them watch a random directory to fix the issue.

Fixes: nodejs#8045

test/parallel/test-fs-watch-recursive.js

@@ -13,14 +13,12 @@ const fs = require('fs');
 
 const testDir = common.tmpDir;
 const filenameOne = 'watch.txt';
-const testsubdirName = 'testsubdir';
-const testsubdir = path.join(testDir, testsubdirName);
-const relativePathOne = path.join('testsubdir', filenameOne);
-const filepathOne = path.join(testsubdir, filenameOne);
 
 common.refreshTmpDir();
 
-fs.mkdirSync(testsubdir, 0o700);
+const testsubdir = fs.mkdtempSync(testDir + path.sep);
+const relativePathOne = path.join(path.basename(testsubdir), filenameOne);
+const filepathOne = path.join(testsubdir, filenameOne);
 
 const watcher = fs.watch(testDir, {recursive: true});
 

test/sequential/test-fs-watch.js

@@ -22,7 +22,7 @@ var filepathTwo = filenameTwo;
 var filepathTwoAbs = path.join(testDir, filenameTwo);
 
 var filenameThree = 'newfile.txt';
-var testsubdir = path.join(testDir, 'testsubdir');
+var testsubdir = fs.mkdtempSync(testDir + path.sep);
 var filepathThree = path.join(testsubdir, filenameThree);