Update use to tolerate errors in develop mode, to prevent buildout from
deleting develop working copies if anything happens, then this behavior was
extended to non-develop mode, apparently by mistake.

In non-develop mode, we want error to propagate, if something went wrong with
updating this repository, buildout should delete and retry.

The purpose is to replace colletive.recipe.shelloutput

/reviewed-on !11

These options were used by a subclass that does not exist anymore.

This reverts the following commits partially:
  d157d8a1
  e92d31cf

With buildout 2, indentation is either fully removed (if anything
starts on the same line as '<option-name> =') or preverved (the same
number of leading spaces if stripped). Any use that required these
commits was a misuse. They could even break valid Python.

This fixes a problem visible when installing openssl 1.1.1d from
component/openssl. At the end of install step, some symlinks are created
inside openssl install directory for all certificates from
ca-certificates part, then the "make read only" step occurs, which
recursively chmod on files and folder in openssl installed parts, but
since this was following symlinks, it was also trying to make readonly
in ca-certificates parts, which in my case was belonging to another
unix user, because it was a shared part folder from outer level slapos.

/reviewed-on !10

It's a nightmare to convert from DOS to GPT (required when moving to a
disk bigger than 2TB), because GRUB can only be installed reliably
from the system to boot.

ext4 was chosen for the 'discard' option, but formatting takes too
much time and space. I was surprised to see my VM being paused
(no left space on host) because of ext4lazyinit.

An unrelated change is about develop mode: the behaviour was simplified to do nothing if a working copy already exists.

TODO: handle removal of submodules

/reviewed-on !7

Note that we don't change the URL for BAD_GIT_REPOSITORY as we need them
to return 500 while trying to clone. If we use Nexedi Gitlab repo for
non-existing repo, we get redirected to login page. Hence, we keep using
git.erp5.org for `repo/nowhere`.

/reviewed-on !6

download, downloadunpacked: Check shared directory is not enough. Shared directory may be created before completing installation. Check signature file too.

Revert "download, downloadunpacked: Check shared directory is not enough. Shared directory may be created before completing installation. Check signature file too."

This reverts commit 9be7928b.

download, downloadunpacked: Check shared directory is not enough. Shared directory may be created before completing installation. Check signature file too.

downloadunpacked: Because shared part should not be uninstalled, install method should return an empty list in shared mode.

download, downloadunpacked: Rename 'shared-part' to 'shared-parts'. Since the original option name is 'parts', 'shared-parts' is consistent.