Fix S3 copy and rename overwriting target directory

Also skip a test for unsupported feature (mtime update of changed directory)

With this the unit tests for S3 pass for me locally.

cc @butonic @DeepDiver1975 
Is there a reason that it defaults to 15 in the constructor below (https://github.com/owncloud/core/pull/10104/files#diff-440d6acd86f4ca1cb35ebcdaaaed8e54R93) but it was changed to 1 here?