When copying an SLO manifest with multipart-manifest=get the actual
manifest content-type should get copied to the destination, rather
than the application/json value that is synthesised by SLO in a GET
response. That way the result of a HEAD on the copied manifest is the
same as a HEAD to the source, and the container listings for the two
are consistent.
This patch also un-skips a functional test and adds functional tests
that verify this patch and also verify that etags and size also get
correctly copied and updated in destination container (bug #1260446).
Closes-Bug: #1260446
Closes-Bug: #1583756
Change-Id: Ie7fa82f70b3ec3ef568f5355c69f6bce460ba25d