modules/smartos_vmadm : add _gen_zone_json(**kwargs) function

_gen_zone_json(**kwargs) will be needed as a template for Zone
creation (aka. OS virtualization). For the moment, only the mandatory
arguments are used.
modules/smartos_vmadm : Fix an incorrect variable
Merge pull request #5273 from virtua-network/vmadm

modules/smartos_vmadm : add _gen_zone_json(**kwargs) function