DEPR/TEST: fix numpy tz-aware parsing warnings
```
/home/travis/build/pydata/pandas/pandas/tseries/tests/test_period.py:420: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
```

full build [here](https://travis-ci.org/pydata/pandas/jobs/103526993)
note this is only on the numpy-dev builds (last 2)

@shoyer recent change to show a deprecation warning on passing tz-aware strings to numpy [here](https://github.com/numpy/numpy/pull/6453) is now causing loads of tests to show these.

so in order to keep backward compat I suppose we need a wrapper function

```
In [1]: np.__version__
Out[1]: '1.12.0.dev0+a38942a'

In [2]: np.datetime64('2007-01-01 09:00:00.001Z')
/Users/jreback/miniconda/envs/numpy_dev/bin/ipython:1: DeprecationWarning: parsing timezone aware datetimes is deprecated; this will raise an error in the future
  #!/bin/bash /Users/jreback/miniconda/envs/numpy_dev/bin/python.app
Out[2]: numpy.datetime64('2007-01-01T09:00:00.001')

In [3]: np.datetime64('2007-01-01 09:00:00.001')
Out[3]: numpy.datetime64('2007-01-01T09:00:00.001')

In [4]: np.datetime64('2007-01-01 09:00:00.001').item()
Out[4]: datetime.datetime(2007, 1, 1, 9, 0, 0, 1000)
```

current numpy

```
In [2]: np.__version__
Out[2]: '1.10.2'

In [3]: np.datetime64('2007-01-01 09:00:00.001Z')
Out[3]: numpy.datetime64('2007-01-01T04:00:00.001-0500')

In [5]: np.datetime64('2007-01-01 09:00:00.001Z').item()
Out[5]: datetime.datetime(2007, 1, 1, 9, 0, 0, 1000)
```

so maybe 

`np_datetime64_compat(....)` that can then introspect our defined `_np_version_under1p11` (define in `pandas/__init__.py`) and add a 'Z' if needed (pre-suppose that we change the input formats to
`2007-01-01 09:00:00.001'`) for clarity.
