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>

cmd/labels/list.go

@@ -5,8 +5,6 @@
 package labels
 
 import (
-	"log"
-
 	"code.gitea.io/tea/cmd/flags"
 	"code.gitea.io/tea/modules/context"
 	"code.gitea.io/tea/modules/print"
@@ -44,7 +42,7 @@ func RunLabelsList(cmd *cli.Context) error {
 		ListOptions: ctx.GetListOptions(),
 	})
 	if err != nil {
-		log.Fatal(err)
+		return err
 	}
 
 	if ctx.IsSet("save") {