adios_comm: close the engine in dtor

[cwsmith]

The ADIOS2 Engine objects need to have Close() called by the user (see my mistake here ornladios/ADIOS2#3269 (comment)).

This PR adds a destructor for the AdiosComm class to close the engine. Following the rule of 5, I explicitly marked the copy/move assignment/constructors as delete as I currently only want users to call CreateAdiosComm(...) and not manipulate individual comm objects.

@jacobmerson Do you see a problem here? Is there a reason to allow AdiosComm object copy/move?

[jacobmerson]

I'm not sure I understand the rational to delete the copy/move constructor/assignment. Is the underlying engine type not copy/movable?

For instance I was moving adios comm out of the comm pair.

[cwsmith]

Discussion offline concluded that we don't know if we can safely copy/move the ADIOS2 Engine and IO objects. This is based on the use of factory methods in the API (i.e., IO::Open to create an Engine, and ADIOS::DeclareIO to create an IO) and the comment in the adios2 docs regarding ownership of IO and Engine objects by the ADIOS instance (https://adios2.readthedocs.io/en/latest/api_full/api_full.html#adios2-components-classes).

Future work may enable/implement these but we currently don't have a need for them.