Allow shell and err_shell commands in a stream too

bin/varnishtest/tests/a02024.vtc

@@ -3,9 +3,14 @@ varnishtest "Write a body to a file"
 server s1 {
 	fatal
 	stream 1 {
+		# First, HTTP checks
 		rxreq
 		expect req.http.Content-Type == "text/plain"
+
+		# Then, payload checks
 		write_body req.txt
+		shell {grep -q request req.txt}
+
 		txresp -hdr Content-Type text/plain -body response
 	} -run
 
@@ -15,13 +20,15 @@ client c1 -connect ${s1_sock} {
 	fatal
 	stream 1 {
 		txreq -req POST -hdr Content-Type text/plain -body request
+
+		# First, HTTP checks
 		rxresp
 		expect resp.http.Content-Type == "text/plain"
+
+		# Then, payload checks
 		write_body resp.txt
+		shell {grep -q response resp.txt}
 	} -run
 } -run
 
 server s1 -wait
-
-shell {grep -q request req.txt}
-shell {grep -q response resp.txt}

bin/varnishtest/vtc_http2.c

@@ -2530,6 +2530,8 @@ static const struct cmds stream_cmds[] = {
 	/* general purpose */
 	CMD(barrier)
 	CMD(delay)
+	CMD(err_shell)
+	CMD(shell)
 	{ NULL,			NULL }
 #undef CMD_STREAM
 #undef CMD