Fixup b3ecd384i (obs/_generic: support bootstrapping with either python2 or python3)

The symbolic link is not suported by re6st compilation (it is totally
removed from the archive)

See merge request nexedi/slapos.package!170

Integrate to generic the new bootstraping method from ```obs/slapos```.
Update some egg versions.

Fixup 33f0e91b (obs/_generic: support | in variables)

Use a non-extended ASCII character. Sed needs a single-byte character as
a separator and extended ASCII is sometimes interpreted as a UTF-8
unicode (which is not single-byte).

Remove "dep--" in the directory and software name.
Set a proper version.
Upgrade to buildout 2.7.1+slapos019

Set a proper version.
Upgrade to buildout 2.7.1+slapos019

...for the purpose of a less obscure and more clear code.

The "dropped Olimex Debian images" are supposed to be very old.
Please see nexedi/slapos.package@7c5a2eff (comment 167627)
for a complete discussion of this decision.

See merge request nexedi/slapos.package!169

 * use cp instead of mv so that the original file doesn't disappear and we
can rerun the script
 * osc rm can fail if the package is empty (especially at creation time
of the package)

Use § for sed separator instead of | so that we can have | in variables.

We need | in PACKAGE_BUILD_DEPENDENCIES of fluent-bit

dep--fluent-bit was just a development package with less dependencies

OBS_PROJECT will be by default the branch project of our production
project : home:VIFIBnexedi:branches:home:VIFIBnexedi

Then if everything compile fine on the branch project, we will submit
the package on OBS website.

See https://www.debian.org/doc/manuals/maint-guide/dother.en.html#dirs

See merge request nexedi/slapos.package!164

lunzip is used as a basic example.

See merge request !168

we use https only starting from debian 11

with backported fixes for debian 11 compatibility