obs/generic/build-scripts/clean_build_tree.sh: Add permissions in go/ directory in order to delete it.

Note: Allow to use custom distribution files instead of the template-generated ones.

templates/: Split into compilation templates and distribution files templates.

distribution-specifics/:
- Remove mca, lunzip and fluent-bit files: they should be generated the same way.
- Add examples files.

build-scripts/:
- Add some variables.
- Add a script for the distribution files.

Makefile:
- Add a stage for distribution files.
- Add a build target: no distrib files generation, no obs.

Warning: General targets tested with lunzip. Reversibility with clean_* untested.

build-scripts/:
- Backup bin/buildout and restore it so that it is not "rebootstraped" when sent to OBS.
- Change some variable names, add a sed regex.

templates/Makefile.in:
- Fix a bug. Add DESTDIR in Makefile.
- Change a variable name.
- Add debugs with ls
distribution-spefcifics/lunzip/debian/dirs: Fix (add / at the beginning)

build-scripts/:
- obs.sh: Fix some bugs.
- configuration-information.sh: Switch version to 1. Tweak some lines.
Warning: switch to mca

distribution-specifics/: Change version from 0-1 to 1-1. (Debian standard doesn't use 0?)

Warning: switched to lunzip.

distribution-specifics/:
- Update the debian/dirs files.
- Change the version and add the version in the name or field where required.

Makefile: Add a target no-obs and its clean_no-obs counterpart.

build-scripts/*:
- Simplify the scripts and add a variable for the path of the current tarball.
- Add new variables and improve the genericization.
build-scripts/obs.sh: Delete .install.cfg in the directory where builtout is run.

templates/*: Improve the templates system: it is no longer needed to modify the templates to build another SR.
templates/Makefile.in: Improve the target management.

templates/Makefile.in:
- Fix a bug:
	Transform templates/Makefile in an actual template Makefile.in leaving less room for path inconsistencies.
- Fix a bug. Remove tmp-networkcached-related commands.

templates/buildout*.in:
- Fix a bug:
	Add the extends-cache and download-cache variables.

build-scripts/template_stage.sh:
	Add support for the new templates/Makefile.in

build-scripts/obs.sh: Fix a bug. Save the path of the local BUILD_DIRECTORY so that it can be replaced in the relevant files by the right path in OBS' VM.
dependencies.txt: Add a dependency.

dependencies.txt lists the dependencies required by the project.

Various fixes. Add OBS stage.
- Remove the top-level Makefile of the archive.
- Rename directories.
- Send directly tarballs/$SOFTWARE.
- Build from tarballs/$SOFTWARE/Makefile.
- Rename variables for clarity.
- Add obs.sh and clean_obs.sh.

- remove template/networkcached.cfg.in
- remove the networkcached support from build_tree.sh and clean_build_tree.sh
- remove the networkcached support from template_stage.sh bootstrap_buildout.sh
- remove cache_creation.sh and clean_cache_creation.sh

The scripts do everything until the first run of buildout (actual run, not just bootstraping).

See merge request nexedi/slapos.package!161

It has more chances to exist than /usr/bin/python executable

This commit also simplifies the preparation of the cache for OBS compilation.

The slapos-node package can be built in any Linux distribution (old or
new).

WARNING: Do not use PYTHON make variable since it messes up with compilation. Instead
use SLAPOS_BOOTSTRAP_SYSTEM_PYTHON which explains the idea of the variable
and does not overrides make's PYTHON variable in other places.

also do not check for invalid certificate in slapos.cfg anymore. It's
been more than 3 years that the certificate is invalid. All our machines
are updated.

For CentOS_8 & CentOS_8_Stream, I give up:
- nothing provides python, python2, python3 or /usr/bin/python
  (actually, there's a python2 package on CentOS_8_Stream, but only to ship
  a /usr/bin/python2 that tells the user not to use Python 2... wtf ?)
- by default, there exists /usr/libexec/platform-python and it's functional
  but the build of openssl requires any of python{,2,3} in PATH, which means
  that a probable solution is to:
  - conditionally depend on 'python' only `%if 0%{?centos_ver} != 8`
  - change Makefile.in to add a symlink to /usr/libexec/platform-python
    in a temporary directory that we add to $PATH during the build
- ... but it's probably fine to use packages for CentOS_7

- Make it compatible with Python 3.
- Install setuptools in a way that's compatible with slapos.rebootstrap
  (otherwise, rebootstrapping fails because signature dependency to
  setuptools changes).

playbook: imt-vm-bootstrap playbook will be called only until success, then it is never called again

This reverts commit 910d2148.

Actually, we will simply stop executing the playbook totally after it is
well configured.