This reverts merge request !243

The first proof of concept  of Caddy in Slapos. 

For now, everything is inside software/caddy but in the next merge request we will move to stack. 

@rafael @romain 


/reviewed-on !243

WIP

  Environment requires new lines instead spaces

   This is required got the usage of git

  MD5SUM update was missing.

Experimental. Not automatically executed.

Restores given backup, configures service as a slave to given master,
starts replication.

Like for "normal" backup restoration, any running mariadb is killed,
started with backup-restoration-friendly parameters, and killed again once
restored.

As there is AFAIK no way to ask supervisor to start even one of our own
services, this script unfortunately leaves the partition in a
not-immediately useful state.

Nothing references this section otherwise.

This value is supposed to come from configuration file, which is already
implicitly provided inside used wrapper.

Back-porting a patch from upstream's github repository.

This reverts commit 18c4c3e2.

  Reduce a little the path+filename for the socket file, as NGINX/Linux has a limitation for long paths on this instruction.

  This small change allow the resilience test works w/o kernel patches or workarrounds.

Now we can run slaprunner's slapos just with `slapos`

For consistency and because mosh uses $SHELL and otherwise would use the
system shell ( /bin/sh )

~/bin/bash was used sometimes in place of bash, but we can use the
"real" bash directly, not need for a wrapper.

Introduce a section to define the shell $PATH and $SHELL we want to reference
from other sections.

slapos.cookbook:shell recipe creates a wrapper copying environment of
user running slapos node instance, but we are trying to avoid this.