This intent to speed up the download (only) of cache by using traffic server

This is implement as a test suite so that it can be automatically on any commit
to rina/slapos repositories.

Currently, the Debian packaging of the kernel only supports Debian Jessie.

This reverts commit 5656363a.

This updates links to slapos.git in the tree to point to new location.

We do so whole-tree except one place in stack/monitor/ :

    [download-monitor-static]
    recipe = hexagonit.recipe.download
    url = http://git.erp5.org/gitweb/slapos.git/snapshot/930be99041ea26b7b1186830e5eb56ef0acc1bdf.tar.gz
    ...

(see d8800c0b "monitor: Download statics files from snapshot")

The reason we do not update that link yet, is that 930be99041ea26b7b1186830e5eb56ef0acc1bdf
is a tree object and gitlab does not allow to dowload tree object as archives (yet ?)

So for now that link stays unconverted - and we'll think how to do with it.

In order to be lighter.