There's a few places where bespoke file-like wrapper classes have been
implemented. The common methods are now inherited from
utils.InputProxy.
Make utils.FileLikeIter tolerate size=None to mean the same as size=-1
so that it is consistent with the behavior of other input streams.
Fix docstrings in FileLikeIter.
Depends-On: https://review.opendev.org/c/openstack/requirements/+/942845
Change-Id: I20741ab58b0933390dc4679c3e6b2d888857d577