The posix and azure backends dropped every upload with a key equal to
the key-marker before handing the list to the lister, which then looked
for the upload-id-marker under the next key. An upload-id-marker that
belongs to the key-marker could never be found, so the request failed
with "Invalid uploadId marker", including when a client paged with the
NextKeyMarker and NextUploadIdMarker the gateway returned.
Keep the uploads of the key-marker itself when an upload-id-marker is
set, so the listing continues right after the given upload, as S3 does.
Enable the REST test that covers it.
Fixes#2149
dualfroz
cbe870a618