add a helper for while loops

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
tests for the new while helper

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
use itertools for seconds sum

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
fix docstring typo

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
Merge pull request #207 from ceph/wip-7356

helper for bombing out of infinite loops