Complex tests generate complex reference values

[ewu63]

Description

Due to the build bot failure last night, we realized that some tests are generating complex values while the reference file contains only the real part. We should fix the tests so that the values we compare are real and not complex.

For IDWarp the following tests are impacted:

test_MultiUSMesh.py:Test_MultiUSMesh_2_complex.test_onera_m6
test_MultiUSMesh.py:Test_MultiUSMesh_3_parallel_complex.test_onera_m6
test_USMesh.py:Test_USmesh_2_complex.test_omesh
test_USMesh.py:Test_USmesh_2_complex.test_sym_mesh
test_USMesh.py:Test_USmesh_3_parallel_complex.test_omesh
test_USMesh.py:Test_USmesh_3_parallel_complex.test_sym_mesh

Steps to reproduce issue

1. Run test_USMesh.py:Test_USmesh_2_complex.test_omesh
2. Look at the value generated for Test_o_mesh - Sum of vCoords Warped

Current behavior

Value is complex

Expected behavior

Value should be real