We used to be able to deep-copy RingBuilder objects, but the addition
of debug logging (8d3b3b2) broke that since you can't deep-copy a
Python logger. This commit fixes that.
Swift doesn't really deep-copy RingBuilders anywhere, but third-party
code might.
Change-Id: If8bdadd93d9980db3d8a093f32d76ca604de9301