Add global comm

[hgangwar]

Moving PR #228 to here for a clean PR.

This PR introduces redev::AdiosGlobalComm to provide a global communication interface between the coupler and the applications using the existing ADIOS channel.
Usage:

auto GDI = app->AddData<pcms::GO>("global_comm", comm);

This creates a global communicator that can send and receive data, for example:

app->BeginSendPhase();
GDI->SendData(mean.data(), "mean", mean.size());
app->EndSendPhase();

app->BeginReceivePhase();
mean = GDI->ReceiveData("mean", mean.size());
app->EndReceivePhase();

• The test_GDI test case verifies global communication and data transfer.

[jacobmerson]

@hgangwar did you update this based on the redev merge? Note, you will need to make sure you bump the redev version in the config files for the CI.

[jacobmerson]

@hgangwar I think we discussed having this owned by the application so we have a consistent API between fields and "global data"

AddField -> AddData
SendField -> SendData
ReceiveField -> ReceiveData

[jacobmerson]

See previous comment about making the API match between fields and global data.

[jacobmerson]

Sorry I did not read carefully, you did add the global data communicator to the application. However for consistency:

• SendData should be a function on the application that takes a string
• Send should be a function on the GDI pointer.

[jacobmerson]

Also, look at how the FieldHandle works. I.e., we return a cheap to copy handle of the field which stores a string which is used to actually perform the send/receive. That way we are not handing a pointer back to the user.