[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/spf13/pflag/int16.go b/vendor/github.com/spf13/pflag/int16.go
new file mode 100644
index 0000000..f1a01d0
--- /dev/null
+++ b/vendor/github.com/spf13/pflag/int16.go
@@ -0,0 +1,88 @@
+package pflag
+
+import "strconv"
+
+// -- int16 Value
+type int16Value int16
+
+func newInt16Value(val int16, p *int16) *int16Value {
+	*p = val
+	return (*int16Value)(p)
+}
+
+func (i *int16Value) Set(s string) error {
+	v, err := strconv.ParseInt(s, 0, 16)
+	*i = int16Value(v)
+	return err
+}
+
+func (i *int16Value) Type() string {
+	return "int16"
+}
+
+func (i *int16Value) String() string { return strconv.FormatInt(int64(*i), 10) }
+
+func int16Conv(sval string) (interface{}, error) {
+	v, err := strconv.ParseInt(sval, 0, 16)
+	if err != nil {
+		return 0, err
+	}
+	return int16(v), nil
+}
+
+// GetInt16 returns the int16 value of a flag with the given name
+func (f *FlagSet) GetInt16(name string) (int16, error) {
+	val, err := f.getFlagType(name, "int16", int16Conv)
+	if err != nil {
+		return 0, err
+	}
+	return val.(int16), nil
+}
+
+// Int16Var defines an int16 flag with specified name, default value, and usage string.
+// The argument p points to an int16 variable in which to store the value of the flag.
+func (f *FlagSet) Int16Var(p *int16, name string, value int16, usage string) {
+	f.VarP(newInt16Value(value, p), name, "", usage)
+}
+
+// Int16VarP is like Int16Var, but accepts a shorthand letter that can be used after a single dash.
+func (f *FlagSet) Int16VarP(p *int16, name, shorthand string, value int16, usage string) {
+	f.VarP(newInt16Value(value, p), name, shorthand, usage)
+}
+
+// Int16Var defines an int16 flag with specified name, default value, and usage string.
+// The argument p points to an int16 variable in which to store the value of the flag.
+func Int16Var(p *int16, name string, value int16, usage string) {
+	CommandLine.VarP(newInt16Value(value, p), name, "", usage)
+}
+
+// Int16VarP is like Int16Var, but accepts a shorthand letter that can be used after a single dash.
+func Int16VarP(p *int16, name, shorthand string, value int16, usage string) {
+	CommandLine.VarP(newInt16Value(value, p), name, shorthand, usage)
+}
+
+// Int16 defines an int16 flag with specified name, default value, and usage string.
+// The return value is the address of an int16 variable that stores the value of the flag.
+func (f *FlagSet) Int16(name string, value int16, usage string) *int16 {
+	p := new(int16)
+	f.Int16VarP(p, name, "", value, usage)
+	return p
+}
+
+// Int16P is like Int16, but accepts a shorthand letter that can be used after a single dash.
+func (f *FlagSet) Int16P(name, shorthand string, value int16, usage string) *int16 {
+	p := new(int16)
+	f.Int16VarP(p, name, shorthand, value, usage)
+	return p
+}
+
+// Int16 defines an int16 flag with specified name, default value, and usage string.
+// The return value is the address of an int16 variable that stores the value of the flag.
+func Int16(name string, value int16, usage string) *int16 {
+	return CommandLine.Int16P(name, "", value, usage)
+}
+
+// Int16P is like Int16, but accepts a shorthand letter that can be used after a single dash.
+func Int16P(name, shorthand string, value int16, usage string) *int16 {
+	return CommandLine.Int16P(name, shorthand, value, usage)
+}