feat(scheduler): gracefully shutdown (#1951)

wait for workers to finish before exiting

should fix tests reporting they couldn't remove rootDir because it's being
written by tasks

Signed-off-by: Petu Eusebiu <peusebiu@cisco.com>

pkg/common/common.go

@@ -1,6 +1,7 @@
 package common
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -135,3 +136,12 @@ func IsReferrersTag(tag string) bool {
 
 	return referrersTagRule.MatchString(tag)
 }
+
+func IsContextDone(ctx context.Context) bool {
+	select {
+	case <-ctx.Done():
+		return true
+	default:
+		return false
+	}
+}