test: fix test-evolve.t Metaedit take the current date when no date is given. When we added default- date, the date ended up to be the same and the behavior changed. Fix the text by disabling default-date in the metaedit call and update the comment about what is needed to fix correctly the test; take the changeset date when metaediting only one changeset.

test: split evolve cycle tests in a separate test file