vtkXOpenGLRenderWindow (0x55f4c3deb260): bad X server connection. DISPLAY=

When running (after applying #358 fix):
```
from dipy.viz import window
ren = window.Renderer()
window.record(ren, n_frames=1, out_path='test.png', size=(600, 600))
```
kernel dies with 
```
ERROR: In /work/standalone-x64-build/VTK-source/Rendering/OpenGL2/vtkXOpenGLRenderWindow.cxx, line 273
vtkXOpenGLRenderWindow (0x55f4c3deb260): bad X server connection. DISPLAY=
```
