Fixes case where shutdown occurs before content is synced to disked
on layer creation. This case can leave the layer store in an bad
state and require manual recovery. This change ensures all files
are synced to disk before a layer is committed. Any shutdown that
occurs will only cause the layer to not show up but will allow it to
be repulled or recreated without error.
Added generic io logic to ioutils package to abstract it out of
the layer store package.
Signed-off-by: Derek McGowan <derek@mcgstyle.net>
c37bd10f8c