bugfix to allow deletion by space to work

Deletion by space doesn't work, and hasn't worked since at least a [huge commit](https://github.com/elasticsearch/curator/commit/73dfa7c8068cdbe2085d732f3822379bf58145a4) in January.

There was a (now deleted) mention that `find_overusage_indices` needed to return a tuple for compatibility.  That was several versions ago and it was abandoned in `find_expired_data`, but I left it alone anyway and just added a tuple check that pulls out the index name.

Please don't add me to contributors.