Refactor error handling (#308)

use fmt instead of log

log.Fatal -> return err

set non-zero exit code on error

print to default err log

cleanup

fix vet

Co-authored-by: Norwin Roosen <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/308
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: 6543 <6543@obermui.de>
Co-Authored-By: Norwin <noerw@noreply.gitea.io>
Co-Committed-By: Norwin <noerw@noreply.gitea.io>

main.go

@@ -1,4 +1,4 @@
-// Copyright 2018 The Gitea Authors. All rights reserved.
+// Copyright 2020 The Gitea Authors. All rights reserved.
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.
 
@@ -6,7 +6,7 @@
 package main // import "code.gitea.io/tea"
 
 import (
-	"log"
+	"fmt"
 	"os"
 	"strings"
 
@@ -25,7 +25,6 @@ func main() {
 	app := cli.NewApp()
 	app.Name = "tea"
 	app.Usage = "Command line tool to interact with Gitea"
-	app.Description = ``
 	app.Version = Version + formatBuiltWith(Tags)
 	app.Commands = []*cli.Command{
 		&cmd.CmdLogin,
@@ -45,7 +44,10 @@ func main() {
 	app.EnableBashCompletion = true
 	err := app.Run(os.Args)
 	if err != nil {
-		log.Fatalf("Failed to run app with %s: %v", os.Args, err)
+		// app.Run already exits for errors implementing ErrorCoder,
+		// so we only handle generic errors with code 1 here.
+		fmt.Fprintf(app.ErrWriter, "Error: %v\n", err)
+		os.Exit(1)
 	}
 }