patchbomb: use `get_unique_pull_path` The patchbomb code does not support multiple destinations yet. It would not be too hard to implemented since `hg outgoing` does. However that is a bit too much of a detour right now. In addition that kind of "select outgoing changesets for processing" code exist for various commands so the best would be to factor it out later. Let us use the dedicated API until this is solved. This comes with a small output change in the test that I find more accurate. So I kept it. Differential Revision: https://phab.mercurial-scm.org/D10405