TST: Testing an installed package shouldn't require root permissions
Trying to run `nosetests3 pandas` on an installed pandas package, I get:

```
ERROR: test_read_dta10 (pandas.io.tests.test_stata.StataTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/pandas/io/tests/test_stata.py", line 207, in test_read_dta10
    original.to_stata(path, {'datetime': 'tc'}, False)
  File "/usr/lib/python3/dist-packages/pandas/core/frame.py", line 1503, in to_stata
    writer = StataWriter(fname,self,convert_dates=convert_dates, encoding=encoding, byteorder=byteorder)
  File "/usr/lib/python3/dist-packages/pandas/io/stata.py", line 745, in __init__
    self._file = _open_file_binary_write(fname, self._encoding)
  File "/usr/lib/python3/dist-packages/pandas/io/stata.py", line 577, in _open_file_binary_write
    return open(fname, "wb")
PermissionError: [Errno 13] Permission denied: '/usr/lib/python3/dist-packages/pandas/io/tests/data/stata10.dta'
```

... and other similar errors. Maybe it'll be a good idea to fix the tests so that they can be run on an installed package without needing to modify the actually installed files.
