NBD server is not running until an image is uploaded. Make sure that the
promise doesn't fail until the image is there. Also display a WARNING in
the connection parameter to say that the NBD server is not running.

When the image is a block device, the guest must also run Linux >= 5.0.

In 95c05120, a published parameter "ssh-url" was added
to the webrunner, clashing with the existing "ssh-url" parameter used by the resilient
stack (which is extended by webrunner).
As the new "ssh-url" is public and read by customers, it doesn't make sense to rename
it to something more slaprunner-ished, more especially it already existis "ssh-command",
so if a second parameter was named "runner-ssh-url" it wouldn't make sense to the user...

This change had to be propagated to all the software releases extending the resilient stack.

Finally, I think that stacks should use namespaces to avoid conflicts with the software
releases extending them. Currently, we are doing the opposite and are using namespaces
for software release to avoid conflicting with their stack : for exemple, in stack/resilient
we have a section [sshd-raw-server] and in the software/slaprunner we have [runner-sshd-raw-server].
This situation will create clashes when one software release extends 2 stacks, as nothing
guarantees that 2 stacks have no conflicting section name, config file path, ...

This reverts commit 4636f49f.

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 nexedi/slapos!512