fixed the output leak from daemon unit tests

Signed-off-by: Arash Deshmeh <adeshmeh@ca.ibm.com>

cmd/docker/daemon_unit_test.go

@@ -3,6 +3,7 @@
 package main
 
 import (
+	"io/ioutil"
 	"testing"
 
 	"github.com/spf13/cobra"
@@ -17,6 +18,7 @@ func TestDaemonCommandHelp(t *testing.T) {
 	cmd := newDaemonCommand()
 	cmd.RunE = stubRun
 	cmd.SetArgs([]string{"--help"})
+	cmd.SetOutput(ioutil.Discard)
 	err := cmd.Execute()
 	assert.NoError(t, err)
 }
@@ -25,6 +27,7 @@ func TestDaemonCommand(t *testing.T) {
 	cmd := newDaemonCommand()
 	cmd.RunE = stubRun
 	cmd.SetArgs([]string{"--containerd", "/foo"})
+	cmd.SetOutput(ioutil.Discard)
 	err := cmd.Execute()
 	assert.NoError(t, err)
 }