Add TestServer (#102)

Add a fullblown testing server. This allows us to do integration tests.

Also add a basic proxy test. Further tests will test etcd proxy
and stub zone communication and other "wildish" configurations.
Redo the server startup, so we can access the ports it listens on when
it has started up (with dns.ActivateAndServer).

Extend the .travis file to download etcd and test for that as well.

Put integration tests in test dir

test/etcd_test.go

@@ -0,0 +1,11 @@
+// +build etcd
+
+package test
+
+import "testing"
+
+// This test starts two coredns servers (and needs etcd). Configure a stubzones in both (that will loop) and
+// will then test if we detect this loop.
+func TestEtcdStubForwarding(t *testing.T) {
+	// TODO(miek)
+}