create a utility to read and return file contents

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
create a mon keyring in a helper function

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
create a mon keyring if not found when deploying a mon

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
Merge pull request #248 from alfredodeza/9662

create a `{cluster}.mon.keyring` file if it doesn't exist