Container servers will store an etag like
<MD5 of manifest on disk>; slo_etag=<MD5 on concatenated ETags>
which the SLO middleware will break out into separate
"hash": "<MD5 of manifest on disk",
"slo_etag": "\"<MD5 of concatenated ETags\"",
keys for JSON listings. Text and XML listings are unaffected.
If a middleware left of SLO already specified a container update
override, the slo_etag parameter will be appended. If the base header
value was blank, the MD5 of the manifest will be inserted.
SLOs that were created on previous versions of Swift will continue to
just have the MD5 of the manifest in container listings.
Closes-Bug: 1618573
Change-Id: I67478923619b00ec1a37d56b6fec6a218453dafc
c4c98eb64d