You can't modify the X-Static-Large-Object metadata with a POST, an
object being a SLO is a property of the .data file. Revert the change
from 4500ff which attempts to correctly handle X-Static-Large-Object
metadata on a POST, but is subject to a race if the most recent SLO
.data isn't available during the POST. Instead this change adjusts the
reading of metadata such that the X-Static-Large-Object metadata is
always preserved from the metadata on the datafile and bleeds through
a .meta if any.
Closes-bug: #1453807
Closes-bug: #1634723
Co-Authored-By: Kota Tsuyuzaki <tsuyuzaki.kota@lab.ntt.co.jp>
Change-Id: Ie48a38442559229a2993443ab0a04dc84717ca59