scripts/analyse-locks-simpletrace.py: script to analyse lock times

This script allows analysis of mutex acquisition and hold times based
on a trace file. Given a trace control file of:

  qemu_mutex_lock
  qemu_mutex_locked
  qemu_mutex_unlock

And running with:

  $QEMU $QEMU_ARGS -trace events=./lock-trace

You can analyse the results with:

  ./scripts/analyse-locks-simpletrace.py trace-events-all ./trace-21812

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>