REGTESTS: add a few load balancing tests

This adds "balance-rr" to test round robin, "balance-uri" to test the
default balance-uri method, and "balance-uri-path-only" which mixes H1
and H2 through "balance uri path-only" and verifies that they reach
the same server.

Note that for the latter, "proto h2" explicitly had to be placed on
the listening socket otherwise it would timeout. This may indicate an
issue in the H1->H2 upgrade depending how the H2 preface is sent maybe.
diff --git a/reg-tests/balance/balance-rr.vtc b/reg-tests/balance/balance-rr.vtc
new file mode 100644
index 0000000..531e84e
--- /dev/null
+++ b/reg-tests/balance/balance-rr.vtc
@@ -0,0 +1,73 @@
+vtest "Test for balance roundrobin"
+feature ignore_unknown_macro
+
+server s1 {
+    rxreq
+    txresp -hdr "Server: s1"
+} -repeat 2 -start
+
+server s2 {
+    rxreq
+    txresp -hdr "Server: s2"
+} -repeat 2 -start
+
+server s3 {
+    rxreq
+    txresp -hdr "Server: s3"
+} -repeat 2 -start
+
+server s4 {
+    rxreq
+    txresp -hdr "Server: s4"
+} -repeat 2 -start
+
+haproxy h1 -arg "-L A" -conf {
+    defaults
+        mode http
+        timeout server 1s
+        timeout connect 1s
+        timeout client 1s
+
+    listen px
+        bind "fd@${px}"
+        balance roundrobin
+        server srv1 ${s1_addr}:${s1_port}
+        server srv2 ${s2_addr}:${s2_port}
+        server srv3 ${s3_addr}:${s3_port}
+        server srv4 ${s4_addr}:${s4_port}
+} -start
+
+client c1 -connect ${h1_px_sock} {
+    txreq -url "/url1"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.Server ~ s1
+} -run
+
+client c2 -connect ${h1_px_sock} {
+    txreq -url "/url1"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.Server ~ s2
+} -run
+
+client c3 -connect ${h1_px_sock} {
+    txreq -url "/url1"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.Server ~ s3
+} -run
+
+client c4 -connect ${h1_px_sock} {
+    txreq -url "/url1"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.Server ~ s4
+} -run
+
+client c5 -connect ${h1_px_sock} {
+    txreq -url "/url1"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.Server ~ s1
+} -run