runstate: Add runstate store

This allows us to store the current state to send it through migration.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

include/sysemu/sysemu.h

@@ -28,6 +28,7 @@ bool runstate_check(RunState state);
 void runstate_set(RunState new_state);
 int runstate_is_running(void);
 bool runstate_needs_reset(void);
+bool runstate_store(char *str, size_t size);
 typedef struct vm_change_state_entry VMChangeStateEntry;
 typedef void VMChangeStateHandler(void *opaque, int running, RunState state);