vl: add runstate_set tracepoint

This patch enables us to know RunState transition. It will be userful
for investigation when the trouble occured in special event such like
live migration, shutdown, suspend, and so on.
Signed-off-by: NKazuya Saito <saito.kazuya@jp.fujitsu.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

trace-events

@@ -474,6 +474,7 @@ scsi_request_sense(int target, int lun, int tag) "target %d lun %d tag %d"
 # vl.c
 vm_state_notify(int running, int reason) "running %d reason %d"
 load_file(const char *name, const char *path) "name %s location %s"
+runstate_set(int new_state) "new state %d"
 
 # block/qcow2.c
 qcow2_writev_start_req(void *co, int64_t sector, int nb_sectors) "co %p sector %" PRIx64 " nb_sectors %d"

vl.c

@@ -642,7 +642,7 @@ void runstate_set(RunState new_state)
                 RunState_lookup[new_state]);
         abort();
     }
-
+    trace_runstate_set(new_state);
     current_run_state = new_state;
 }