restapi: add support to regenerate ids when adding vm from configuration

This patch adds support to regenerate new ids when adding a vm from
the configuration. This is done so that the vm could be still added from
a provided configuration even if the "original" vm still exists.

Change-Id: I9ccf0f61b58ad49aa50d1efe3aa0b9a8bd31da70
Signed-off-by: Liron Aravot <laravot@redhat.com>