build-using-dockerfile: add --annotation

Add an --annotation flag to "buildah build-using-dockerfile".

Refactor the logic for --label handling to use SetLabel() to set them in
the image configuration in Executor.Commit(), instead of passing them as
a field in CommitOptions for Builder.Commit() and expecting it to do so.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #716
Approved by: rhatdan

commit.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"strings"
 	"time"
 
 	cp "github.com/containers/image/copy"
@@ -53,8 +52,6 @@ type CommitOptions struct {
 	// Squash tells the builder to produce an image with a single layer
 	// instead of with possibly more than one layer.
 	Squash bool
-	// Labels metadata for an image
-	Labels []string
 }
 
 // PushOptions can be used to alter how an image is copied somewhere.
@@ -89,15 +86,6 @@ type PushOptions struct {
 func (b *Builder) Commit(ctx context.Context, dest types.ImageReference, options CommitOptions) (string, error) {
 	var imgID string
 
-	for _, labelSpec := range options.Labels {
-		label := strings.SplitN(labelSpec, "=", 2)
-		if len(label) > 1 {
-			b.SetLabel(label[0], label[1])
-		} else {
-			b.SetLabel(label[0], "")
-		}
-	}
-
 	systemContext := getSystemContext(options.SystemContext, options.SignaturePolicyPath)
 	policy, err := signature.DefaultPolicy(systemContext)
 	if err != nil {