[Fix] Doc

Issue: - It is not possible to pass [R]andom [N]umber [G]enerator
         device to libvirt guest xml in order to control entropy.

       - Doc has no information on how to provision vms using salt

Solution: - Pass rng parameters via kwargs from node: pillar
            Attach rng xml object to generated xml.

          - Provide with an example

Prod-Related: PROD-19214
Customer-Found
Change-Id: Iea111f2d927edf46f06bb7ccfad06d37b752fba9