testing: Switch inline engine test MPI usage based on libraries linked
testing: Switch inline engine test MPI usage based on libraries linked

This was accidentally left out of commit b5dd8b164 (testing: Switch
C/C++ test MPI usage based on libraries linked, 2020-04-20).

JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,ornladios/ADIOS2,ornladios/ADIOS2