[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/dustin/go-humanize/ftoa.go b/vendor/github.com/dustin/go-humanize/ftoa.go
new file mode 100644
index 0000000..c76190b
--- /dev/null
+++ b/vendor/github.com/dustin/go-humanize/ftoa.go
@@ -0,0 +1,23 @@
+package humanize
+
+import "strconv"
+
+func stripTrailingZeros(s string) string {
+	offset := len(s) - 1
+	for offset > 0 {
+		if s[offset] == '.' {
+			offset--
+			break
+		}
+		if s[offset] != '0' {
+			break
+		}
+		offset--
+	}
+	return s[:offset+1]
+}
+
+// Ftoa converts a float to a string with no trailing zeros.
+func Ftoa(num float64) string {
+	return stripTrailingZeros(strconv.FormatFloat(num, 'f', 6, 64))
+}