Merged requested to merge 732-test_ff_stokes_channel_3d-fails-with-different-velocity into master
[freeflow][test] In channel 3d test use smaller Newton tolerance. This way, velocities in y and z direction, which should be zero, assume values smaller 1e-12 which is the tolerance for comparing the test solution against the reference solution. Additionally, adapt the reference solution.
Closes #732 (closed)