Previously, we'd preserve the sysmeta that we wrote down with the
original multipart-upload to track its S3-style etag on the new part,
causing it to have an ETag like `<MD5>-<N>`. Later, when the client
tried to complete the new multipart-upload, it would send that etag back
to the server, which would reject the request because the ETag didn't
look like a normal MD5.
Now, have s3api include blank values in the copy request to overwrite
the source sysmeta, and treat a blank etag override the same as a
missing one.
Change-Id: Id33a7ab9d0b8f33fede73eae540d6137708e1218
Closes-Bug: #1829959
e22960fd71