Vector animation implementation needs finishing

[chaosphere2112]

#1450 removes the VTK pipeline rebuilding code from VTKPlots.py, and with it goes a partial implementation for vector plots. I've ported this bit into unmerged commit 1ffc97a6e029d3988be8b26df3b4713ffa083181 (branch https://github.com/UV-CDAT/uvcdat/tree/update_input_vector), made sure a complete pipeline would persist through the animation steps, and added a test.

Migrated from: CDAT/cdat#1451

[doutriaux1]

on nightly i get:

import vcs, cdms2, MV2                                                                                                                                                                                                 
import cdat_info  ; f = cdms2.open(cdat_info.get_sampledata_path()+"/clt.nc")                                                                                                                                          
u = f("u")                                                                                                                                                                                                             
v = f("v")                                                                                                                                                                                                             
gm = vcs.createvector()                                                                                                                                                                                                
x = vcs.init()                                                                                                                                                                                                         
x.plot(u,v,gm)                                                                                                                                                                                                         
x.interact()                                                                                                                                                                                                          

Then click [configure]->[Open Animation]->[Run]

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
/1TB/git/vcs/vcs/configurator.py in animate(self, obj, event)
    702                 self.canvas.animate.number_of_frames(),
    703                 render_offscreen=False,
--> 704                 allow_static=False)
    705 
    706     def start_animating(self):

/1TB/git/vcs/vcs/VTKAnimate.py in draw_frame(self, frame_num, render_offscreen, allow_static, main_window_png)
    315                 self._number_of_dims_used_for_plot,
    316                 frame_num,
--> 317                 update=False)
    318 
    319             self.vcs_self.backend.renWin.Render()

/1TB/git/vcs/vcs/VTKAnimate.py in update_input(canvas, dimensions, frame_num, update)
     42                 slabs[1](
     43                     *args),
---> 44                 update=update)
     45 
     46 

/1TB/git/vcs/vcs/VTKPlots.py in update_input(self, vtkobjects, array1, array2, update)
   1759             vcs2vtk.setArray(vg, array1.filled(0).flat, "scalar",
   1760                              isCellData=vg.GetCellData().GetScalars(),
-> 1761                              isScalars=True)
   1762 
   1763             if "vtk_backend_filter" in vtkobjects:

/1TB/git/vcs/vcs/vcs2vtk.py in setArray(grid, array, arrayName, isCellData, isScalars)
    214     if (pedigreeId):
    215         vtkarray = attributes.GetArray(arrayName)
--> 216         for i in range(0, vtkarray.GetNumberOfTuples()):
    217             vtkarray.SetValue(i, array[pedigreeId.GetValue(i)])
    218     else:

AttributeError: 'NoneType' object has no attribute 'GetNumberOfTuples'