Add options for build squashing

Related to docker/docker#22641

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

client/image_build.go

@@ -74,6 +74,10 @@ func imageBuildOptionsToQuery(options types.ImageBuildOptions) (url.Values, erro
 		query.Set("pull", "1")
 	}
 
+	if options.Squash {
+		query.Set("squash", "1")
+	}
+
 	if !container.Isolation.IsDefault(options.Isolation) {
 		query.Set("isolation", string(options.Isolation))
 	}

types/client.go

@@ -147,6 +147,10 @@ type ImageBuildOptions struct {
 	AuthConfigs    map[string]AuthConfig
 	Context        io.Reader
 	Labels         map[string]string
+	// squash the resulting image's layers to the parent
+	// preserves the original image and creates a new one from the parent with all
+	// the changes applied to a single layer
+	Squash bool
 }
 
 // ImageBuildResponse holds information