test: refresh the tmpdir before using

Test fails if tmp dir does not exist when the test is run. Add
common.refreshTmpDir() so that doesn't happen.

PR-URL: nodejs#7327
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

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

@@ -10,6 +10,8 @@ if (common.isFreeBSD) {
   return;
 }
 
+common.refreshTmpDir();
+
 const fn = '新建文夹件.txt';
 const a = path.join(common.tmpDir, fn);