Add our own labels to container cpu memory related metrics

[gocodersuresh]

Hi
Currently we are exporting metric using caadvisor for cpu and memory usage.
Issue is we want to know which user is using which container when he uses our application
We want to add user=userid in each system metric system metric meaning metric which are related to cpu usageheap memory usage,disk usage

[gocodersuresh]

@dims @mrunalp @pmorie how about adding labels by polling message queue