Intermittent cleaner test failure

```
  1) Content Cleaner verify only old files get removed:
      
      actual expected
      
      /tmp/oae/tests
      
  AssertionError: "/tmp/oae" == "/tmp/oae/tests"
      at EventEmitter.<anonymous> (/home/travis/build/oaeproject/Hilary/node_modules/oae-util/tests/test-cleaner.js:93:24)
      at EventEmitter.g (events.js:192:14)
      at EventEmitter.emit (events.js:96:17)
      at cleanDirectory (/home/travis/build/oaeproject/Hilary/node_modules/oae-util/lib/cleaner.js:81:21)
      at checkFiles (/home/travis/build/oaeproject/Hilary/node_modules/oae-util/lib/cleaner.js:127:16)
      at checkFiles (/home/travis/build/oaeproject/Hilary/node_modules/oae-util/lib/cleaner.js:135:9)
      at checkFile (/home/travis/build/oaeproject/Hilary/node_modules/oae-util/lib/cleaner.js:112:13)
      at Object.oncomplete (fs.js:297:15)
```

I think this is because the test assumes there is only cleaner running, which is not the case. There are 3 other cleaner processes running:
 * General temporary files
 * Uploaded files
 * Preview files