[master] d4cf677ae vtc: Stabilize a21

[Dridi Boukelmoune]

commit d4cf677ae48a46317bab432104c3729913d7a9db
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Fri May 28 14:34:59 2021 +0200

    vtc: Stabilize a21
    
    And make a note that we should avoid pthread_cancel(3) in the future.

diff --git a/bin/varnishtest/tests/a00021.vtc b/bin/varnishtest/tests/a00021.vtc
index 9eb158582..43688b0f8 100644
--- a/bin/varnishtest/tests/a00021.vtc
+++ b/bin/varnishtest/tests/a00021.vtc
@@ -44,3 +44,5 @@ client c2 -connect "${t2_sock}" {
 	txreq
 	rxresp
 } -run
+
+tunnel t2 -wait