[T] Line source tests in 3d cube domain.

...term_middle/3D_line_source_term_pcs_0_ts_1_t_1.000000.vtu

...m_tests/3D_line_source_term_middle/cube_1x1x1_hex_1e3.vtu

...s/3D_line_source_term_middle/cube_1x1x1_hex_1e3_right.vtu

..._tests/3D_line_source_term_middle/line_at_x_0.5_y_0.5.vtu

..._line_source_term_middle/line_source_term_x_0.5_y_0.5.prj

.../3D_line_source_term_restricted_pcs_0_ts_1_t_1.000000.vtu

...line_source_term_middle_restricted/cube_1x1x1_hex_1e3.vtu

...ource_term_middle_restricted/cube_1x1x1_hex_1e3_right.vtu

...term_middle_restricted/line_at_x_0.5_y_0.5_restricted.vtu

...le_restricted/line_source_term_x_0.5_y_0.5_restricted.prj