Extend redset test suite

[adammoody]

More tests to be added to redset:

• [ ] Modify test so that it can run on a single host (avoid using hostname to split into redundancy groups).
• [ ] Add a test where different ranks write a different number of files, and include a case where one rank writes 0 files.
• [ ] Assign different groups to different files with chown(), and check that proper group is restored after rebuilding a deleted file.
• [ ] Create a test in which COMM_WORLD is divided into multiple redundancy sets. Delete files from one set so that it can't be recovered. Verify that all ranks in COMM_WORLD identify that the rebuild failed.
• [ ] Test that serial rebuilds work for all redundancy schemes.
• [ ] Run valgrind to check for memory leaks.

Resolve issues noted in:

• [x] https://github.com/ECP-VeloC/redset/issues/20
• [ ] https://github.com/ECP-VeloC/redset/issues/30

[adammoody]

@CamStan and @kosinovsky , I'm creating a running list of new tests we should eventually add to redset. These might also apply to other components like shuffle and axl, but I'll just keep the running list in redset for now. Once we implement these in redset, we can just cut-and-paste them to the other components or perhaps define a new testutils repo that our different components could share.