qmp/migration: new command migrate-recover

The first allow-oob=true command.  It's used on destination side when
the postcopy migration is paused and ready for a recovery.  After
execution, a new migration channel will be established for postcopy to
continue.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180502104740.12123-21-peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
---
s/2.12/2.13/
diff --git a/migration/migration.h b/migration/migration.h
index b4438cc..f83f106 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -77,6 +77,7 @@
     struct PostcopyBlocktimeContext *blocktime_ctx;
 
     /* notify PAUSED postcopy incoming migrations to try to continue */
+    bool postcopy_recover_triggered;
     QemuSemaphore postcopy_pause_sem_dst;
     QemuSemaphore postcopy_pause_sem_fault;
 };