Parallel test on Ubuntu works with mshr, not with xml.

mpi_test.py doesn't run, fenics_mpi_example runs with mpirun -n 4 python3 fenics_mpi_example.py
and scales well with number of cores. mpi_test.py gives error point outside domain when run in
parallel, but works well single core.

test_mpi.py

+from fem_sol import frap_solver
+f_0 = frap_solver([4, 4, 0.5], 'Meshes/single_drop_coverslip.xml',
+                          name='FRAP_coverslip', T=300, phi_tot_ext=0.001)
+f_0.solve_frap()