- compat level was missing
- keep debconf disabled
- skip shlibs

Plus some clean up.

  Changes are from slapos.git repository.

Since buildout 2 no longer supports using multiple versions of Python
in a single buildout, we're now forced to use slapos.rebootstrap.

I found that include paths of slapos package's perl were wrong (i.e. `/usr/src/packages/BUILD/SLAPOS/build` should be removed).

```
~> /opt/slapos/parts/perl/bin/perl -e 'print @INC,"\n"'
/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/site_perl/lib/site_perl/5.20.2/x86_64-linux-thread-multi/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/site_perl/lib/site_perl/5.20.2/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/perl/lib/5.20.2/x86_64-linux-thread-multi/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/perl/lib/5.20.2.
```

I think that this MR fixes this issue but not so sure. Can you please verify it ?

/cc @alain.takoudjou @rafael 

/reviewed-on nexedi/slapos.package!23

because for Debian, 0.479+slapos.gfd8673b is newer than 0.479+slapos2.g12d4231

 OpenSSL is broken inside rebootstrap folder as it cannot find appropriate
 openssl.cnf . This should be solved at buildout level however it might
 require way too much hours of debug. Please revert this change as soon
 buildout includes appropriate fix.

  As the distribution contains older python the code assertion fail on some test files, remove them is safe

  else the more recents rpm based linux cannot build packages.

This simplifies the procedure to debug.