[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/go.etcd.io/bbolt/bolt_ppc64.go b/vendor/go.etcd.io/bbolt/bolt_ppc64.go
new file mode 100644
index 0000000..3565908
--- /dev/null
+++ b/vendor/go.etcd.io/bbolt/bolt_ppc64.go
@@ -0,0 +1,12 @@
+// +build ppc64
+
+package bbolt
+
+// maxMapSize represents the largest mmap size supported by Bolt.
+const maxMapSize = 0xFFFFFFFFFFFF // 256TB
+
+// maxAllocSize is the size used when creating array pointers.
+const maxAllocSize = 0x7FFFFFFF
+
+// Are unaligned load/stores broken on this arch?
+var brokenUnaligned = false