Handle system termination signals (#152)

Currently termination can only be forced (as the context that is used to determine cancellation is never actually cancelled). This PR closes the context on termination signals from the OS.

This should reduce the runtime of tests especially (as a significant amount of time is spent on waiting for workflows process to finish after a SIGTERM.

cmd/fission-workflows-bundle/main.go

@@ -4,6 +4,9 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"os/signal"
+	"syscall"
+	"time"
 
 	"github.com/fission/fission-workflows/cmd/fission-workflows-bundle/bundle"
 	"github.com/fission/fission-workflows/pkg/fes/backend/nats"
@@ -14,7 +17,21 @@ import (
 )
 
 func main() {
-	ctx := context.Background()
+	ctx, cancelFn := context.WithCancel(context.Background())
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt, os.Kill, syscall.SIGTERM)
+	go func() {
+		for sig := range c {
+			fmt.Println("Received signal: ", sig)
+			go func() {
+				time.Sleep(30 * time.Second)
+				fmt.Println("Deadline exceeded; forcing shutdown.")
+				os.Exit(0)
+			}()
+			cancelFn()
+			break
+		}
+	}()
 
 	cliApp := createCli()
 	cliApp.Action = func(c *cli.Context) error {