ssync rx sends a header X-Backend-Replication-Headers whose value is a
list of headers that the source object has. This list extends the list
of allowed headers on the target object server, so that the target
object metadata is faithfully reconstructed to match the source.
Unfortunately the combination of lower() and title() operations on
header keys results in the source 'ETag' value being added to the target
metadata under the key 'Etag' in addition to the 'ETag' key that the
receiving server adds (note different capitilization), both having
the same value.
The spurious 'Etag' metadata is potentially confusing for humans
inspecting the object metadata and complicates tests that wish to
assert the equality of two object metadata dicts. See for example the
test in test_ssync_sender.py that this patch cleans up.
Furthermore, the possibility of having both Etag and ETag keys has
required a workaround in the EC reconstructor [1].
[1] reconstructor fix change id: Ie59ad93a67a7f439c9a84cd9cff31540f97f334a
Change-Id: I0c89cf7924a4471bb6d268b5ef3884e2d2cb4286
6f89f71f9b