YANG model for SR OS on VSR does not include 'power-shelf' -> get_environment fails

[jbemmel]

https://github.com/napalm-automation-community/napalm-sros/blob/287ed784399eefddd9aad5f32692b6161bbdcfaf/napalm_sros/nc_filters.py#L927

In 21.10 it's power-shelf: https://github.com/nokia/7x50_YangModels/blob/master/latest_sros_21.10/nokia-state-chassis.yang#L1460 however for some reason on VSR there is only (emulated) power-supply

Consequently, get_environment fails completely, even though other information like CPU/memory utilization is available