Adjust error cases for which we now receive a 500 response

src/tests/backref_limit.vtc

@@ -131,12 +131,14 @@ logexpect l1 -v v1 -d 0 -g vxid -q "VCL_Error" {
 
 client c2 {
 	txreq -hdr "Int11: 12"
-	expect_close
+	rxresp
+	expect resp.status == 500
 } -run
 
 client c3 {
 	txreq -hdr "Int20: 21"
-	expect_close
+	rxresp
+	expect resp.status == 500
 } -run
 
 logexpect l1 -wait

src/tests/cost.vtc

@@ -49,7 +49,8 @@ client c1 {
 
 client c1 {
 	txreq -hdr "Fail: oops"
-	expect_close
+	rxresp
+	expect resp.status == 500
 } -run
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {

src/tests/match.vtc

@@ -86,7 +86,8 @@ varnish v1 -vcl {
 
 client c2 {
 	txreq
-	expect_close
+	rxresp
+	expect resp.status == "500"
 } -run
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {