import fails after clean anaconda install
#### Code Sample, a copy-pastable example if possible

```python
>>> import pandas
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/hanan/anaconda3/lib/python3.6/site-packages/pandas/__init__.py", line 59, in <module>
    from pandas.util._tester import test
  File "/home/hanan/anaconda3/lib/python3.6/site-packages/pandas/util/_tester.py", line 11, in <module>
    import pytest
  File "/home/hanan/anaconda3/lib/python3.6/site-packages/pytest.py", line 27, in <module>
    _preloadplugins() # to populate pytest.* namespace so help(pytest) works
  File "/home/hanan/anaconda3/lib/python3.6/site-packages/_pytest/config.py", line 109, in _preloadplugins
    _preinit.append(get_config())
  File "/home/hanan/anaconda3/lib/python3.6/site-packages/_pytest/config.py", line 118, in get_config
    pluginmanager.import_plugin(spec)
  File "/home/hanan/anaconda3/lib/python3.6/site-packages/_pytest/config.py", line 426, in import_plugin
    __import__(importspec)
  File "/home/hanan/anaconda3/lib/python3.6/site-packages/_pytest/debugging.py", line 3, in <module>
    import pdb
  File "/home/hanan/anaconda3/lib/python3.6/pdb.py", line 136, in <module>
    class Pdb(bdb.Bdb, cmd.Cmd):
AttributeError: module 'cmd' has no attribute 'Cmd'

```
#### Problem description

import fails on a clean install of anaconda

#### Expected Output

import success silently
 
#### Output of ``pd.show_versions()``

<details>
# Paste the output here pd.show_versions() here
import fails, instead I grep pandas from `conda list`
pandas                    0.20.1              np112py36_0  

</details>
