Second attempt at preventing zombies (#16326)

* Second attempt at preventing zombies

* Ensure that the pipes are closed in ssh.go
* Ensure that a cancellable context is passed up in cmd/* http requests
* Make cmd.fail return properly so defers are obeyed
* Ensure that something is sent to stdout in case of blocks here

Signed-off-by: Andrew Thornton <art27@cantab.net>

* placate lint

Signed-off-by: Andrew Thornton <art27@cantab.net>

* placate lint 2

Signed-off-by: Andrew Thornton <art27@cantab.net>

* placate lint 3

Signed-off-by: Andrew Thornton <art27@cantab.net>

* fixup

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Apply suggestions from code review

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lauris BH <lauris@nix.lv>

cmd/cmd.go

@@ -7,9 +7,13 @@
 package cmd
 
 import (
+	"context"
 	"errors"
 	"fmt"
+	"os"
+	"os/signal"
 	"strings"
+	"syscall"
 
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/setting"
@@ -66,3 +70,25 @@ func initDBDisableConsole(disableConsole bool) error {
 	}
 	return nil
 }
+
+func installSignals() (context.Context, context.CancelFunc) {
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		// install notify
+		signalChannel := make(chan os.Signal, 1)
+
+		signal.Notify(
+			signalChannel,
+			syscall.SIGINT,
+			syscall.SIGTERM,
+		)
+		select {
+		case <-signalChannel:
+		case <-ctx.Done():
+		}
+		cancel()
+		signal.Reset()
+	}()
+
+	return ctx, cancel
+}