lxml web site, provided by index, is not functional for long time (weeks).
As it is possible to install it directly form pypi (which has a bit of
mirroring) force such way and do not query source website.

As zabbix agentd cannot run in foreground mode wrap it in simple foreground
application which sends singals whenever it is requested to be killed.

Instantiation shall depend on minimal tools, like system administrator would.

This reverts commit 5c763b0089dbdf355c0efe8830e808e9580735f6.
We keep slapos.recipe.download in slapos.cookbook