fn: cleanup of docker private registry code (#1130)

* fn: cleanup of docker private registry code

Start using URL parsed ServerAddress and its subdomains
for easier image ensure/pull in docker driver. Previous
code to lookup substrings was faulty without proper
URL parse and hostname tokenization. When searching
for a registry config, if image name does not contain
a registry and if there's a private registry configured,
then search for hub.docker.com and index.docker.io. This
is similar to previous code but with correct subdomain
matching.

* fn-dataplane: take port into account in auth configs

api/agent/drivers/docker/registry_test.go

@@ -0,0 +1,59 @@
+package docker
+
+import (
+	"testing"
+)
+
+func verify(expected []string, checks map[string]bool) bool {
+	if len(expected) != len(checks) {
+		return false
+	}
+	for _, v := range expected {
+		_, ok := checks[v]
+		if !ok {
+			return false
+		}
+	}
+	return true
+}
+
+func TestRegistrySubDomains(t *testing.T) {
+	var exp []string
+	var res map[string]bool
+
+	exp = []string{"google.com"}
+	res = getSubdomains("google.com")
+	if !verify(exp, res) {
+		t.Fatalf("subdomain results failed expected[%+v] != results[%+v]", exp, res)
+	}
+
+	exp = []string{"top.google.com", "google.com"}
+	res = getSubdomains("top.google.com")
+	if !verify(exp, res) {
+		t.Fatalf("subdomain results failed expected[%+v] != results[%+v]", exp, res)
+	}
+
+	exp = []string{"top.google.com:443", "google.com:443"}
+	res = getSubdomains("top.google.com:443")
+	if !verify(exp, res) {
+		t.Fatalf("subdomain results failed expected[%+v] != results[%+v]", exp, res)
+	}
+
+	exp = []string{"top.top.google.com", "top.google.com", "google.com"}
+	res = getSubdomains("top.top.google.com")
+	if !verify(exp, res) {
+		t.Fatalf("subdomain results failed expected[%+v] != results[%+v]", exp, res)
+	}
+
+	exp = []string{"docker"}
+	res = getSubdomains("docker")
+	if !verify(exp, res) {
+		t.Fatalf("subdomain results failed expected[%+v] != results[%+v]", exp, res)
+	}
+
+	exp = []string{""}
+	res = getSubdomains("")
+	if !verify(exp, res) {
+		t.Fatalf("subdomain results failed expected[%+v] != results[%+v]", exp, res)
+	}
+}