lib/repo: Enforce min-free-space-* size check for regfiles in deltas

lib/repo: Enforce min-free-space-* size check for regfiles in deltas

During the pull, there is an explicit check for free space on disk
vs. the size of uncompressed delta; But while writing the new content
objects that are generated, they have to honor min-free-space-* checks
too. We enforce this check in _bare_content_commit as that is where
we can know the final size of the new content object.

Closes: #1614
Approved by: jlebon