make sure we pass the --cluster flag

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
update the changelog

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
Merge pull request #49 from alfredodeza/5499

`osd` should honor the `--cluster` flag and use it (fixes 5499)