Merge remote-tracking branch 'stefanha/tracing' into staging

# By Lluís Vilanova (7) and others
# Via Stefan Hajnoczi
* stefanha/tracing:
  vl: add runstate_set tracepoint
  .gitignore: rename trace/generated-tracers.dtrace
  .gitignore: add trace/generated-events.[ch]
  trace: rebuild generated-events.o when configuration changes
  trace: [stderr] Port to generic event information and new control interface
  trace: [simple] Port to generic event information and new control interface
  trace: [default] Port to generic event information and new control interface
  trace: [monitor] Use new event control interface
  trace: Provide a detailed event control interface
  trace: Provide a generic tracing event descriptor
  trace: [tracetool] Explicitly identify public backends