fix(config) error when specifying port for cassandra_contact_point

cassandra_contact_point does not tolerate port specification.
Issue an error when the user specifies it by mistake.

kong/conf_loader.lua

@@ -183,6 +183,18 @@ local function check_and_infer(conf)
                         "DCAwareRoundRobin policy is in use"
   end
 
+  for _, contact_point in ipairs(conf.cassandra_contact_points) do
+    local endpoint, err = utils.normalize_ip(contact_point)
+    if not endpoint then
+      errors[#errors+1] = "bad cassandra contact point '" .. contact_point ..
+                          "': " .. err
+
+    elseif endpoint.port then
+      errors[#errors+1] = "bad cassandra contact point '" .. contact_point ..
+                          "': port must be specified in cassandra_port"
+    end
+  end
+
   if conf.ssl then
     if conf.ssl_cert and not conf.ssl_cert_key then
       errors[#errors+1] = "ssl_cert_key must be specified"

spec/01-unit/02-conf_loader_spec.lua

@@ -262,6 +262,20 @@ describe("Configuration loader", function()
       assert.is_nil(err)
       assert.is_table(conf)
     end)
+    it("errors when hosts have a bad format in cassandra_contact_points", function()
+      local conf, err = conf_loader(nil, {
+          cassandra_contact_points = [[some/really\bad/host\name,addr2]]
+      })
+      assert.equal([[bad cassandra contact point 'some/really\bad/host\name': invalid hostname: some/really\bad/host\name]], err)
+      assert.is_nil(conf)
+    end)
+    it("errors when specifying a port in cassandra_contact_points", function()
+      local conf, err = conf_loader(nil, {
+          cassandra_contact_points = "addr1:9042,addr2"
+      })
+      assert.equal("bad cassandra contact point 'addr1:9042': port must be specified in cassandra_port", err)
+      assert.is_nil(conf)
+    end)
     it("cluster_ttl_on_failure cannot be lower than 60 seconds", function()
       local conf, err = conf_loader(nil, {
         cluster_ttl_on_failure = 40