Fix an error in test_group
Fix an error in test_group

The new position set commands wrap particles, so the points at the right
edge of the box got wrapped to the left making apparent failures in
the test_group test.

joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue