Fix non default tenant and HTTPS support

Using Bosch IOT Rollout server implies to use a specific `tenant`, which
currently fails with message `401 Unauthorized`.
Setting tenant to another value then DEFAULT is not used.

HTTPS artifact URL is provided in `download` entry, while HTTP one is
provided in `download-http`.  Add HTTPS url support and try to use it in
first intention.

Use g_autoptr for JSon builder, generator and node

Signed-off-by: Frédéric Danis <frederic.danis@collabora.com>