Jupyter: Switch to using JSON in instance parameters

The reason is: we are going to integrate Jupyter into ERP5 SR, and in
ERP5 SR code, there is already established infrastructure, which
requests slave instances. That infrastructure passes parameters in
serialized (= json) form, that's why we need to switch.

On the other hand, slapos.cookbook:slapconfiguration.serialised handles
non-json instance parameters as well: when there parameters format is
not

    {'_' -> <json>}

it decodes them as slapos.cookbook:slapconfiguration would do:

    https://lab.nexedi.com/nexedi/slapos/blob/69229988/slapos/recipe/slapconfiguration.py#L232
    https://lab.nexedi.com/nexedi/slapos/blob/69229988/slapos/recipe/librecipe/__init__.py#L51

So from this point of view, though we don't really need it here (Jupyter
SR is relatively new), we are staying backward compatible.

/cc @tiwariayush

software/ipython_notebook/instance.cfg.in

@@ -34,7 +34,7 @@ develop-eggs-directory = {{ develop_eggs_directory }}
 offline = true
 
 [slapconfiguration]
-recipe = slapos.cookbook:slapconfiguration
+recipe = slapos.cookbook:slapconfiguration.serialised
 computer = ${slap-connection:computer-id}
 partition = ${slap-connection:partition-id}
 url = ${slap-connection:server-url}

software/ipython_notebook/software.cfg

@@ -60,7 +60,7 @@ recipe = slapos.recipe.template:jinja2
 template = ${:_profile_base_location_}/instance.cfg.in
 rendered = ${buildout:directory}/template.cfg
 mode = 0644
-md5sum = 1a993b1f8fa3f001c45075fe95a48332
+md5sum = 0186ead0c3596e847b69ff8040a43a2f
 context =
   key bin_directory buildout:bin-directory
   key develop_eggs_directory buildout:develop-eggs-directory