No OpenMPI build variant

[jbweston]

• [x] I read the conda-forge documentation and could not find the solution for my problem there.

Issue:

There is no OpenMPI build variant for this package (only mpich or nompi). This is not a high priority issue, but may be important for users who wish to install Kwant alongside software that only works with OpenMPI.

We had to disable building the OpenMPI variant, as tests failed in a strange way when building the package:

Environment (conda list):

``` $ conda list ```

Details about conda and system ( conda info ):

``` $ conda info ```

[jbweston]

We can look here to see how to solved this: https://github.com/conda-forge/fenics-feedstock/pull/140

Specifically, it seems we need to set some environment variables when testing (this is specific to the environment that the conda package is built in, and does not need to be done by end users):

        - export OMPI_MCA_plm=isolated  # [mpi == 'openmpi']
        - export OMPI_MCA_btl_vader_single_copy_mechanism=none  # [mpi == 'openmpi']
        - export OMPI_MCA_rmaps_base_oversubscribe=yes  # [mpi == 'openmpi']
        - export OMPI_MCA_plm_rsh_agent=$CONDA_PREFIX/bin/false  # [mpi == 'openmpi']
        - export OMPI_MCA_btl_base_warn_component_unused=0  # [mpi == 'openmpi']