add test case by @rezan

bin/varnishtest/tests/r03009.vtc

+varnishtest "Rollback without restart/retry is unsafe"
+
+server s1 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+	import std;
+
+	sub vcl_recv {
+		set req.http.test = "1";
+	}
+
+	sub vcl_backend_fetch {
+		unset bereq.http.test;
+	}
+
+	sub vcl_backend_response {
+		std.rollback(bereq);
+		set beresp.http.test = bereq.http.test;
+		set beresp.http.workspace = "start overwriting active workspace";
+		set beresp.http.workspace = "0123456789012345678901234567890123456789";
+		# panic...
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.http.test == "1"
+} -run