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 ( 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)

Our schemas test check all files if they are present, but it so far it did not check
that the request and response schema referenced in software.cfg.json were really
existing and they were missing for some softwares.

This extends the test to check that request / response exists and add missing responses for cdn-me and srslte

See merge request nexedi/slapos!910

So that the test fail if they are missing.

monitor_v6_url and info_1 were not documented, monitor_v6_url is useless
since we have monitor_url and info_1 seems "self explanatory" for humans
and not targeted at machines.

also fix typo on publish-connection-informations

It's empty because the instance does not publish anything at this point.

See merge request nexedi/slapos!892

It allows to access monitoring with a monitoring web app.

If the service crash it will inform master by trigger a "bang" call

Learn more by reading: README.update-hash.rst