Workload hooks: instrumented Scheduler

[dhschall]

We have workitems as trigger points already integrated for instrumentation on the client side.
As istrumentation on the server side we want to add workload hooks. Which can be used to attach probe points to the linux scheduler.

• Need to build kernel with ThreadInfo #50
• Add gem5 fork to vswarm-u #34
• Alternatively add it via EXTRAS for the beginning
• Integrate the workload hooks from serverless-perf to vswarm-u
• Add documentation