Add copyOutput option to globalFluxInterface

[mgjarrett]

Description

Add option not to copy the output back from globalFluxInterface.

Sometimes the globalFluxInterface is only run to get a k-eigenvalue for a given case. Even if this is the case, the globalFluxInterface will still copy the full output from the physics kernel back to the working directory, which can be 50 MB+. When running many hundreds or thousands of cases to calculate k-effective from various perturbations, this generates an unwieldly number and total size of output files that aren't needed. The noOutput option would allow a case to call the globalFluxInterface, grab k-effective from the output, and then skip the step of copying it back to the working directory.

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[mgjarrett]

Only a single line was added, and it is in an __init__ function that is already covered. No new unit tests are needed to cover this feature.

[albeanth]

@mgjarrett and I are currently discussing the effects this has on downstream applications. Once that has been settled, we will move forward with this PR.

[albeanth]

Docstring looks incomplete?