Mayavi off screen rendering not working for VTK 7.1.0

I use vtk with the MesaOS driver as I want to run the rendering as part of a jupyter notebook in headless mode, some more details to the package configuration can be found here:
https://github.com/conda-forge/vtk-feedstock/issues/20

When I use the VTK off screen example it is working fine:
```
#! ./local/bin/python

from vtk import (vtkSphereSource, vtkPolyDataMapper, vtkActor, vtkRenderer,
vtkRenderWindow, vtkWindowToImageFilter, vtkPNGWriter)

sphereSource = vtkSphereSource()
mapper = vtkPolyDataMapper()
mapper.SetInputConnection(sphereSource.GetOutputPort())

actor = vtkActor()
actor.SetMapper(mapper)

renderer = vtkRenderer()
renderWindow = vtkRenderWindow()
renderWindow.SetOffScreenRendering(1)
renderWindow.AddRenderer(renderer)

renderer.AddActor(actor)
renderer.SetBackground(1, 1, 1)

renderWindow.Render()

windowToImageFilter = vtkWindowToImageFilter()
windowToImageFilter.SetInput(renderWindow)
windowToImageFilter.Update()

writer = vtkPNGWriter()
writer.SetFileName("sphere.png")
writer.SetInputConnection(windowToImageFilter.GetOutputPort())
writer.Write()
```

But when I test the mayavi off screen example, it is not working:
```
# Author: Prabhu Ramachandran
# Copyright (c) 2007, Enthought, Inc.
# License: BSD Style.

from os.path import join, abspath, dirname

# The offscreen Engine.
from mayavi.api import OffScreenEngine

# Usual MayaVi imports
from mayavi.scripts.util import get_data_dir
from mayavi.sources.api import VTKXMLFileReader
from mayavi.modules.api import Outline, ScalarCutPlane, Streamline

def main():
# Create the MayaVi offscreen engine and start it.
e = OffScreenEngine()
# Starting the engine registers the engine with the registry and
# notifies others that the engine is ready.
e.start()

# Create a new scene.
win = e.new_scene()

# Now setup a normal MayaVi pipeline.
src = VTKXMLFileReader()
src.initialize(join(get_data_dir(dirname(abspath(__file__))),
'fire_ug.vtu'))
e.add_source(src)
e.add_module(Outline())
e.add_module(ScalarCutPlane())
e.add_module(Streamline())
win.scene.isometric_view()
# Change the size argument to anything you want.
win.scene.save('offscreen.png', size=(800, 800))

if __name__ == '__main__':
main()
```

The error message I get is:
```
ERROR: In ../Rendering/OpenGL2/vtkXOpenGLRenderWindow.cxx, line 301
vtkXOpenGLRenderWindow (0x30ced20): bad X server connection. DISPLAY=Aborted
```

So to me it seems like the off screen initialisation is not correctly forwarded to VTK. Unfortunately I was unable to locate the initialisation of VTK inside mayavi myself. To me it seems to be happening in `tvtk_access.py`, still I do not see an option to force offscreen rendering directly.