python or python2 is system python, which we want to avoid

Co-authored-by: Kazuhiko SHIOZAKI <kazuhiko@nexedi.com>

This reverts commit b2db18a0cb672204ff1dd9bc759934b332d433f5.

This contain the fix for go 1.16 that we backported, so we can use
upstream repository again

For now this still have to be enabled with a config like this in a .conf
file in srv/telegraf/extra-config/  :

    [[inputs.execd]]
      name_override = "slapos"
      # this needs sudo when using can not access supervisor socket, like when being installed in root slapos
      command = ["/usr/bin/sudo", "$SOFTWARE_DIR/go.work/bin/telegraf-input-slapos", "-config", "/path/to/slapos.conf"]

/path/to/slapos.conf would contain something like this:

    [[inputs.slapos]]
      ## Folder where partitions are located
      instance_root = "/srv/slapgrid/"

      ## filepath.Glob pattern to look for recursive instances
      recursive_instance_glob_pattern = "*/srv/runner/inst*/"

      ## Path of supervisor socket, relative to instance root
      socket_name = "sv.sock"

This version has a new sql input, that can be used to get metrics from sql
queries.

starting coverage in runUnitTest was too late, coverage has to be
started before anything is imported for correct reporting

Since slapos.core!436 requesting with `--parameters-file` requires
that a JSON schema exists at <sr-url>.json for the requested SR.

Missing trailing /

See nexedi/slapos@5e1ff2de

zlib source url has been moved. Please see issue
https://github.com/madler/zlib/issues/649 for reference.

See merge request nexedi/slapos!1276