tools lib traceevent: Add back in kvm plugins nested_vmexit events

The nested vmexit events were removed from the backport from trace-cmd because
they were considered buggy. They have since been updated in trace-cmd but
are still missing from the traceevent library. Add back in the buggy
version to be able to backport the fixes.

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20140613021157.291421941@goodmis.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>