Sometimes virtual timer callbacks depend on order
of virtual timer processing and warping of virtual clock.
Therefore every callback should be logged to make replay deterministic.
This patch creates a checkpoint before every virtual timer callback.
With these checkpoints virtual timers processing and clock warping
events order is completely deterministic.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Acked-by: Alex Bennée <alex.bennee@linaro.org>

--

v2:
  - remove mutex lock/unlock for virtual clock checkpoint since it is
    not process any asynchronous events (commit ca9759c2)
  - bump record/replay log file version
Message-Id: <159012932716.27256.8854065545365559921.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>