Fixed assertions in client-server with MantaView.

vtkMantaRenderer had a typo and was incorrectly reporting the type of the
renderer. This was causing the asserts in vtkSynchronizedRenderers since it
erroneously concluded that vtkMantaRenderer was not a vtkOpenGLRenderer. This
fixes that issue.

Change-Id: Idd10ba2f6151465f9227a5006b82f5279d334f41
Merge topic 'fix_manta_view_client_server' into next

7012d2c Fixed assertions in client-server with MantaView.