Add vinit in tests/caf/presentation/begin

All "caf presentation" tests fail on Linux with this error
message:
  AISInitViewer D
  0:
  There is the empty 3D viewer
  Executing .../tests/caf/presentation/end...
  vdump .../results/caf/presentation/A1.png
  Cannot find an active viewer/view

  Tcl Exception: Cannot find an active viewer/view