run-tests: rely on an actual executable in PATH instead of alias for `hg` The alias approach is poorly inherited by other process that the test might spawn. To solve this we use the same approach as for `python`/`python3` we write an executable file explicitly. Doing this fixes `which hg` invocation that now returns the same location as `hg`. Using chg server side has some minor effect on some stdout/stderr ordering when using `chg` as the server too. Differential Revision: https://phab.mercurial-scm.org/D11053

tests: blacklist a handful of test with `rhg` or `chg` The use of `alias` to enforce `chg` and `rhg` means we are actually using a mix of `rhg`/`chg` and `hg` when calling `hg` in the test. Fixing this breaks various tests. This would be a large detour to fix that. I am disabling them for now with an appropriate comment. We would hopefully get back to them by the 5.8 release. Differential Revision: https://phab.mercurial-scm.org/D11052

run-tests: use more explicit signaling for `chg` Using a dedicated variable is clearer and less fragile. It cannot hurt. Differential Revision: https://phab.mercurial-scm.org/D11051