osbuild: add variadic version of Pipeline.AddStage() method

This will allow to conveniently add multiple stages to the pipeline at
once, which is useful if a generator function wrapping some
functionality generates more than one `Stage`.

Signed-off-by: Tomáš Hozza <thozza@redhat.com>

internal/osbuild/osbuild.go

@@ -36,3 +36,12 @@ func (p *Pipeline) AddStage(stage *Stage) {
 		p.Stages = append(p.Stages, stage)
 	}
 }
+
+// AddStages appends multiple stages to the list of stages of a pipeline. The
+// stages will be executed in the order they are appended.
+// If the argument is nil, it is not added.
+func (p *Pipeline) AddStages(stages ...*Stage) {
+	for _, stage := range stages {
+		p.AddStage(stage)
+	}
+}