REGTEST: lua: check socket functionality from a lua-task

Adding a new test /reg-tests/lua/b00004.vtc which checks if the core.tcp()
socket basic functions properly when used from a lua-task
diff --git a/reg-tests/lua/b00004.vtc b/reg-tests/lua/b00004.vtc
new file mode 100644
index 0000000..91b5dde
--- /dev/null
+++ b/reg-tests/lua/b00004.vtc
@@ -0,0 +1,34 @@
+varnishtest "Lua: check socket functionality from a lua-task"
+feature ignore_unknown_macro
+
+#REQUIRE_OPTIONS=LUA
+#REQUIRE_VERSION=1.6
+
+server s1 {
+    rxreq
+    txresp -bodylen 20
+} -start
+
+haproxy h1 -conf {
+    global
+        lua-load ${testdir}/b00004.lua
+
+    frontend fe1
+        mode http
+        bind "fd@${fe1}"
+        default_backend b1
+
+    backend b1
+        mode http
+        http-request use-service lua.fakeserv
+
+} -start
+
+client c0 -connect ${h1_fe1_sock} {
+    txreq -url "/" -hdr "vtcport: ${s1_port}"
+    rxresp
+    expect resp.status == 200
+} -run
+
+
+server s1 -wait
\ No newline at end of file