Add processstats.py to collect informations about running processes

The following informations are collected:
- Number of running KVM processes
- CPU and memory statistics per KVM process, the kvm process can be
  identified with the following tags:
  - pid
  - If "-uuid" was passed to the KVM cmdline, the UUID is recorded
    as tag
- Number of running tcollector processes
- CPU and memory statistics of tcollector and his hardworking child
  processes.
  To identify a tcollector process the name of the executable is
  recorded in the name tag.

Metrics:
 - kvm.cputime
 - kvm.mem_bytes
 - kvm.processes
 - tcollector.cputime
 - tcollector.mem_bytes