Added utils.FileLikeIter

A really simple version of this was in container sync already, and I
needed a more complete version for work I'm doing, and I noticed
https://review.openstack.org/#/c/33405/ was also making use of it.
So, here's a more full version.

If https://review.openstack.org/#/c/33405/ lands before this, I'll
update it accordingly.

Change-Id: Iba66b6a97f65e312e04fdba273e8f4ad1d3e1594
Merge "Added utils.FileLikeIter"