* Also store shared instance list after retrieving it

See merge request !1268

When using pre-commit hook (the one installed by using `npm install`
from the root of the repository), all .json files are checked to be
valid json and formatted according to the ./format-json rules.

These templates were problematic for this script because they are not
really valid json, so name them .json.jinja2 instead of .jinja2.json so
that they are not selected by the pre-commit hook

See merge request nexedi/slapos!1262

See merge request nexedi/slapos!1267

Move hardcoded values to default values.
Source the whole content of the data-to-vm parameter.

See merge request nexedi/slapos!1266