added CPU service to PSet configuration

As discussed in this HN
https://hypernews.cern.ch/HyperNews/CMS/get/edmFramework/3352/1.html

this is how we populate FJR with basic CPU info. Just tested this in testbed, here is
the outcome example [1].
I'll make another PR for the master branch later on. Thanks

```
[1]
<PerformanceReport>
  <PerformanceSummary Metric="SystemCPU">
    <Metric Name="CPUModels" Value="Quad-Core AMD Opteron(tm) Processor 2389"/>
    <Metric Name="averageCoreSpeed" Value="2637.5"/>
    <Metric Name="totalCPUs" Value="8"/>
  </PerformanceSummary>
</PerformanceReport>
```