[Core][MPI] Partially adapt CppTestsUtilities for MPI

[loumalouomega]

📝 Description

This PR adapts to functions in CppTestsUtilities in order to be MPI ready.

🆕 Changelog

• Partially adapt CppTestsUtilities for MPI

[roigcarlo]

Could you explain a bit why you have made some of the decisions here?

• Why serial / distributed is different?
• In parallel, why nodes 1 to 4 are created both in rank 0 and 1 but not in the rest? and why the 5 to 8 are created in rank 1? Does it mean this will only work with world size 2?
• Why the elements are created in rank 1 and none of them in rank 0 in parallel but in rank 0 in serial?

Maybe an example on how this will be used in parallel would help?

[loumalouomega]

Could you explain a bit why you have made some of the decisions here?

* Why serial / distributed is different?

* In parallel, why nodes 1 to 4 are created both in rank 0 and 1 but not in the rest? and why the 5 to 8 are created in rank 1? Does it mean this will only work with world size 2?

* Why the elements are created in rank 1 and none of them in rank 0 in parallel but in rank 0 in serial?

Maybe an example on how this will be used in parallel would help?

It is a synthetic model part I create for certain Cpp tests. I only do 0 partitions when worl size = 1, and 2 partitions otherwise (more partititions would be complicated). Just that. It is used in the same places these methods are used in serial but for MPI tests.