Fix task status unit test dependency

It depends on couch_log to be running. Otherwise it
throw this error:

```
unexpected termination of test process*
::{{badmatch,undefined},
   [{couch_log,debug,2,[{file,"src/couch_log.erl"},{line,32}]},
    {couch_task_status,handle_cast,2,
                       [{file,"src/couch_task_status.erl"},{line,137}]},
```

And only 6 out of 11 tests are run.

COUCHDB-2832
1 file changed
tree: b61bdd4416d2a36ec02a3b29ec564bb53ceefdf5
  1. include/
  2. priv/
  3. src/
  4. test/
  5. .gitignore
  6. LICENSE
  7. rebar.config.script