frontend-instance-guid and frontend-additional-instance-guid are used to
control where the websocket frontend shall end up.

Real frontend is always requested.

Additional frontend is requested only if frontend-additional-instance-guid is
not empty. This frontend is published as url-additional and can be used for
access to users from some restricted networks.

publish-early does not work in this case, and monitor password is stored
in buildout elsewhere anyway.

Prevent creating 2 wrapper for the same service if hash changed. Here, one service is exited because port is used by the firt to service to start:

    slappart6:runner-sshd-4248650e36a9a26a6481df1baffd9f58-on-watch                RUNNING   pid 27835, uptime 0:03:45
    slappart6:runner-sshd-b3b68f4278ceb84691ec27521ea229eb-on-watch                EXITED    Mar 06 04:52 PM

To achieve that, update slapos.cookbook and use hash-existing-files option of wrapper recipe

hash-existing-files list all the files used for hash that are not
handled by buildout. For those files, the hash is calculated as soon as
the __init__ function so that if there is a change in those files,
buildout will remove the existing wrapper (it will uninstall the
section) and replace it with the new wrapper.

/reviewed-on nexedi/slapos!525

otherwise it will stall VM execution.

This is observed inside qemu VM started by 

https://lab.nexedi.com/nexedi/slapos/blob/master/software/erp5testnode/testsuite/deploy-test/software.cfg

In qemu log one can see:
===
QEMU waiting for connection on: disconnected:unix:/srv/slapgrid/slappart6/var/qmp_socket,server

===

Affected version:

root@z600:/srv/slapgrid/slappart6# /opt/slapgrid/7903668a197f3cf8f94375d0739a21e8/parts/kvm/bin/qemu-system-x86_64 --version
QEMU emulator version 2.8.0
Copyright (c) 2003-2016 Fabrice Bellard and the QEMU Project developer

/reviewed-on nexedi/slapos!585

/cc @rafael @jm @alain.takoudjou 

Here we go

/reviewed-on nexedi/slapos!529

use address 1 instead of address 0 and display a /etc/network/interfaces syntax.

Also display the info for resilient KVM.

Note that formatting is not perfect due to softwaretype recipe (which doesn't preserve spaces).

/cc @jm @rafael @alain.takoudjou

/reviewed-on nexedi/slapos!521

Close the NBD socket when testing it so it won't mess up qemu.

/reviewed-on nexedi/slapos!516

- Add `buildout.hash.cfg` file so this way we can use the useful `update-hash` script
- Refactor a bit the `software.cfg` file sections as it was repeating itself

/reviewed-on !512