ui: Support colored output on Windows

This commit uses the go-colorable library to enable support for coloured
UI output on Windows. This acts as a compatibility layer that takes
standard unix-y terminal codes and translates them into the requisite
windows calls as required.

command/commands.go

@@ -7,6 +7,7 @@ import (
 	"github.com/hashicorp/nomad/command/agent"
 	"github.com/hashicorp/nomad/drivers/docker/docklog"
 	"github.com/hashicorp/nomad/version"
+	colorable "github.com/mattn/go-colorable"
 	"github.com/mitchellh/cli"
 )
 
@@ -63,8 +64,8 @@ func Commands(metaPtr *Meta, agentUi cli.Ui) map[string]cli.CommandFactory {
 	if meta.Ui == nil {
 		meta.Ui = &cli.BasicUi{
 			Reader:      os.Stdin,
-			Writer:      os.Stdout,
-			ErrorWriter: os.Stderr,
+			Writer:      colorable.NewColorableStdout(),
+			ErrorWriter: colorable.NewColorableStderr(),
 		}
 	}
 

main.go

@@ -12,6 +12,7 @@ import (
 	"github.com/hashicorp/nomad/command"
 	"github.com/hashicorp/nomad/drivers/docker/docklog"
 	"github.com/hashicorp/nomad/version"
+	"github.com/mattn/go-colorable"
 	"github.com/mitchellh/cli"
 	"github.com/sean-/seed"
 	"golang.org/x/crypto/ssh/terminal"
@@ -91,8 +92,8 @@ func RunCustom(args []string) int {
 	isTerminal := terminal.IsTerminal(int(os.Stdout.Fd()))
 	metaPtr.Ui = &cli.BasicUi{
 		Reader:      os.Stdin,
-		Writer:      os.Stdout,
-		ErrorWriter: os.Stderr,
+		Writer:      colorable.NewColorableStdout(),
+		ErrorWriter: colorable.NewColorableStderr(),
 	}
 
 	// The Nomad agent never outputs color