migration: force QEMUFile to blocking mode for outgoing migration

Instead of relying on the default QEMUFile I/O blocking flag
state, explicitly turn on blocking I/O for outgoing migration
since it takes place in a background thread.
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Message-Id: <1461751518-12128-8-git-send-email-berrange@redhat.com>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>

migration/migration.c

@@ -1791,6 +1791,7 @@ void migrate_fd_connect(MigrationState *s)
     s->expected_downtime = max_downtime/1000000;
     s->cleanup_bh = qemu_bh_new(migrate_fd_cleanup, s);
 
+    qemu_file_set_blocking(s->to_dst_file, true);
     qemu_file_set_rate_limit(s->to_dst_file,
                              s->bandwidth_limit / XFER_LIMIT_RATIO);