Adds more tests for blockstructuring, stokes not working

test/blockstructured/CMakeLists.txt

test/blockstructured/nonlinear/CMakeLists.txt

test/blockstructured/nonlinear/nonlinear.mini

test/blockstructured/nonlinear/nonlinear.ufl

test/blockstructured/poisson/CMakeLists.txt

test/blockstructured/poisson/poisson.mini

test/blockstructured/poisson/poisson.ufl

test/blockstructured/poisson/poisson_matrix_free.mini

test/blockstructured/poisson/poisson_neumann.mini

test/blockstructured/poisson/poisson_neumann.ufl

test/blockstructured/stokes/CMakeLists.txt

test/blockstructured/stokes/hagenpoiseuille_ref.vtu

test/blockstructured/stokes/stokes.mini

test/blockstructured/stokes/stokes.ufl