small bugs in test case MblkLinAdv

small bugs in test case MblkLinAdv.
1. MblkLinAdv.C Line 571 & 572. It should be d_center[1] and d_center[2]
2. Test input octant_3blk.3d.input. The Multiblock GridGeometry is not correctly mapped to the physical xyz coordinates in MblkGeometry.C. i.e., the neighbourhood relation in octant_3blk.3d.input is not the same as the physical neighbourhood relation when it is constructed by MblkGeometry.C. It could be fixed by exchanging Block 1 and Block 2 in octant_3blk.3d.input.

Start with MblkLinAdv.C lines 571-572 and the octant_3blk.3d.input test input, then inspect MblkGeometry.C to compare block mappings with physical xyz neighborhoods. Done means correcting the two d_center references and making the input's neighborhood relation match the physical relation constructed by MblkGeometry.C.

Written by the indexing model from the issue text.