jsonnet/node-exporter: adjust to node-exporter v1.2.0 arg name change

In version [node-exporter v1.2.0](https://github.com/prometheus/node_exporter/releases/tag/v1.2.0

)
two argument name changes were introduced. While the old names still
work (with a deprecation warning), lets use the new names.

Signed-off-by: Jan Fajerski <jfajersk@redhat.com>