testing: switch to inserting deltas As the comment in the test specifies, this was relying on storage backend implementation details. We switch to inserting a raw delta, skipping the regular insert path to ensure we have the desired outcome. This required implementing support for handling deltas in the revlog testing code. Differential Revision: https://phab.mercurial-scm.org/D5116

testing: remove expectation of error on bad node insert addgroup() doesn't necessarily validate the hashes of each incoming revision. This is an optimization that allows delta group application to complete faster. The fact that revlog raises in this particular test is an implementation detail due to the way revlogs are testing multiple deltas. Differential Revision: https://phab.mercurial-scm.org/D5115