Rename test output file of mpi_create_partitioning

As per
https://github.com/dealii/dealii/pull/9991#discussion_r418361364

diff --git a/tests/base/mpi_create_partitioning_01.output b/tests/base/mpi_create_partitioning_01.mpirun=1.output
similarity index 100%
rename from tests/base/mpi_create_partitioning_01.output
rename to tests/base/mpi_create_partitioning_01.mpirun=1.output