Maintain consistency with the slapOS SR format.
This SR can be hooked with other SR(ex:wendelin) and its better
to follow one way of publishing result parameters

[ kirr: This essentially changes publication format to JSON:

    $ xslapos proxy show --params

    # before
    slappart0: ipython_notebook (type default)
        url = https://[2001:67c:1254:e:49::952d]:8888
        monitor_url = https://[2001:67c:1254:e:49::952d]:9685

    # after
    slappart0: ipython_notebook (type default)
        _ = {"url": "https://[2001:67c:1254:e:49::952d]:8888", "monitor_url": "https://[2001:67c:1254:e:49::952d]:9685"}

  I'm not convinced we really need this, nor that the .serialized version is
  the most oftenly used one:

    slapos$ git grep 'slapos.cookbook:publish$' |wc -l
    59
    slapos$ git grep 'slapos.cookbook:publish.serialised$' |wc -l
    13

  but we can have it and see how it goes, reverting if needed ]

/cc @jerome
/proposed-for-review-on !33