tvtk scene windows blank/unresponsive

```

import os
assert(os.environ['ETS_TOOLKIT'] == 'qt4')
from mayavi import mlab
mlab.test_plot3d()
```

generates blank/unresponsive figure window

My system info is:

> Platform: Linux-4.4.0-87-generic-x86_64-with-debian-stretch-sid
> Python: 2.7.13 |Continuum Analytics, Inc.| (default, Dec 20 2016, 23:09:15) [GCC 4.4.7 20120313 (Red Hat 4.4.7-1)]
> Executable: /home/ktavabi/miniconda3/envs/py2.7/bin/python
> CPU: x86_64: 24 cores
> Memory: 94.4 GB
> mne: 0.15.dev0
> numpy: 1.13.1 {lapack=mkl_intel_lp64, blas=mkl_intel_lp64}
> scipy: 0.19.1
> matplotlib: 2.0.2
> sklearn: 0.18.2
> nibabel: 2.1.0
> mayavi: 4.5.0
> pycuda: 2017.1
> skcuda: 0.5.1
> pandas: 0.20.3

cc @Eric89GXL