[VOL-2193] Create mocks for Kafka Client and Etcd

This commit consists of:
1) A kafka client mock that implements the kafka client interface
under voltha-lib-go/pkg/kafka/client.go
2) An embedded Etcd server that runs in-process and represents an
Etcd server.

Change-Id: I52a36132568e08c596bb4136918bebcb654a3b99
diff --git a/vendor/github.com/modern-go/reflect2/go_above_19.go b/vendor/github.com/modern-go/reflect2/go_above_19.go
new file mode 100644
index 0000000..c7e3b78
--- /dev/null
+++ b/vendor/github.com/modern-go/reflect2/go_above_19.go
@@ -0,0 +1,14 @@
+//+build go1.9
+
+package reflect2
+
+import (
+	"unsafe"
+)
+
+//go:linkname makemap reflect.makemap
+func makemap(rtype unsafe.Pointer, cap int) (m unsafe.Pointer)
+
+func makeMapWithSize(rtype unsafe.Pointer, cap int) unsafe.Pointer {
+	return makemap(rtype, cap)
+}