tests: several failures on Cray clusters

Test suite fails on a Cray with several errors similar to:

 ✗ paraview/cone serial
   (in test file [...]/examples/mpi/paraview/test.bats, line 34)
     `ch-run $ch_unslurm -b "$indir" -b "$outdir" "$ch_img" -- \' failed
   --------------------------------------------------------------------------
   The application appears to have been direct launched using "aprun",
   but OMPI was not built with ALPS support. This usually happens
   when OMPI was not configured --with-alps and we weren't able
   to discover an ALPS installation in the usual places.

   Please configure as appropriate and try again.
   --------------------------------------------------------------------------
   *** An error occurred in MPI_Init
   *** on a NULL communicator
   *** MPI_ERRORS_ARE_FATAL (processes in this communicator will now abort,
   ***    and potentially your MPI job)
   [nid00089:58834] Local abort before MPI_INIT completed completed successfully, but am not able to aggregate error messages, and not able to guarantee that all other processes were killed!

I wonder if $ch_unslurm in test/common.bash needs to have more variables excluded?

For now, I'm skipping these tests on Cray.