The metering-agent service is an optional service to gather metrics in
Telemetry(ceilometer + gnocchi), thus is usually disabled if Telemetry
is disabled.
This change disables the service in the scenarios without Telemetry so
that we can validate deployments without this optional service.
Change-Id: I6f1bb575b891318ac83e26450d7b0699a1911b66
891c32918a