Changes:
- Add comments and reorganise instance.cfg.in for clarity
- Select free ports instead of hardcoded ports
- Upgrade to slapos.core 1.6.5 to prefix forwarded requests

This makes it possible to recursively nest theias into theias.

See merge request nexedi/slapos!919

Not sure which commit broke it, but this diff is now polluting my commits.

GOPATH is going to be removed in Go1.17 (see e.g. https://github.com/golang/go/issues/37755#issuecomment-771879911).

-> Prevent programs suddenly become installed into $HOME/go/bin instead of
gowork/bin, and mod cache to become something like $HOME/go/... instead of
being kept under gowork/

No change in behaviour for Go ≤ 1.16

This reverts commit 685f611d partially
because it breaks Mroonga (https://github.com/mroonga/mroonga/pull/394).
It's not so urgent to upgrade MariaDB so let's wait for a new release
of Mroonga.

Go1.16 is incremental improvement over Go1.15 with better and faster compiler,
runtime and module-mode improvements:

https://blog.golang.org/go1.16
https://golang.org/doc/go1.16

Since this Go release switches GO111MODULE default from "auto" to "on", but we
still have in-tree GOPATH-mode uses, add GO111MODULE=auto to our goenv.sh to
preserve previous behaviour for now.

Don't drop support for Go1.14, Go1.13, Go1.12 yet, as that no longer supported
Go releases are still being used by in-tree components(*).

Remain default at Go1.15 yet.

Switch helloworld to Go1.16 and test this patch on that
software-release.

(*) theia, caddy, galene, replication-manager, restic, gitlab and grafana

Go1.14 is end-of-life by today as it will no longer be updated after Go1.16 was
released in Feb 2021:

        https://golang.org/doc/devel/release.html#go1.14
        https://golang.org/doc/devel/release.html#go1.16

Go1.15 is current oldstable - i.e. it is still supported and mature.

Going Go1.14.12 -> Go1.14.15 brings in fixes to compiler, runtime, standard
library and build security.

https://golang.org/doc/devel/release.html#go1.14.minor

Tested on helloworld SR (by adjusting it to use go1.14 instead of go1.15)

Go1.14.15 is the last Go1.14.x release, because, after Go1.16 was released, Go1.14
becomes end-of-life and will not receive any updates nor fixes for security bugs.

/cc @jerome (for theia which is on go1.14)
/cc @luke (for caddy which is on go1.14)

/cc @tomo, @alain.takoudjou (for galene which is still on EOL go1.13)
/cc @alain.takoudjou (for replication-manager which is still on EOL go1.13)
/cc @alain.takoudjou (for restic which is still on EOL go1.13)

/cc @jerome, @alain.takoudjou (for gitlab which is still on EOL go1.12)
/cc @jerome (for grafana which is still on EOL go1.12)

Going Go1.15.5 -> 1.15.8 brings in fixes to compiler, runtime, standard library
and build security.

https://golang.org/doc/devel/release.html#go1.15.minor

Tested on helloworld SR.

* Update md5sum
* Add extra egg plone command

This brings in the following changes:

- nexedi/nxdtest@1e6a1cc6
- nexedi/nxdtest@b5a74214

The first one makes nxdtest more robust to detect an error in its worker
thread, while the second one makes nxdtest more human-friendly when used
while developing.

/reviewed-by @jerome
/reviewed-on nexedi/slapos!918

buildout has no knowledge of setup_requires, when installing a package with
setup_requires, setuptools will fetch the package from pypi and install its latest
version, regardless of buildout's versions or allow-picked-versions options, that
are critical for us to ensure repeatability.

These patches were produced by running buildout with a modified setuptools version which does not install setup_requires ( jerome/setuptools@54f42c38 ) and by modifying the profiles to use setup-eggs option in all the sections installing packages using setup_requires.

See merge request nexedi/slapos!912

It does -X PUT + --data-binary @file.

It's available only on the slave, so it is not part of master partition
configuration.

Due to the cleanup change the parameter parsing logic has to be improved.

Improvements:

 * link from README to schemas
 * drop incorrect entries in README
 * improve entries description in README
 * make parameter description more understandable in SCHEMA

Instead of duplicating the versions and having an old pin to a version
which is now older than caucase minimum required version.

This reverts commit 16d90017
because new use of collective.recipe.template is forbidden.

use six for python3 compatibility

See merge request nexedi/slapos!914

See merge request nexedi/slapos!913

All CMF Products are using eggtestinfo as a setup egg (which is
no longer the case after 2.4.0)