Restructure and polish docker code

Restructure and polish docker code to fix a package tangle and
provide better separation of concerns.

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/build/Builder.java

@@ -21,10 +21,10 @@
 
 import org.springframework.boot.buildpack.platform.build.BuilderMetadata.Stack;
 import org.springframework.boot.buildpack.platform.docker.DockerApi;
-import org.springframework.boot.buildpack.platform.docker.DockerException;
 import org.springframework.boot.buildpack.platform.docker.TotalProgressEvent;
 import org.springframework.boot.buildpack.platform.docker.TotalProgressPullListener;
 import org.springframework.boot.buildpack.platform.docker.UpdateListener;
+import org.springframework.boot.buildpack.platform.docker.transport.DockerEngineException;
 import org.springframework.boot.buildpack.platform.docker.type.Image;
 import org.springframework.boot.buildpack.platform.docker.type.ImageReference;
 import org.springframework.util.Assert;
@@ -56,7 +56,7 @@ public Builder(BuildLog log) {
 		this.docker = docker;
 	}
 
-	public void build(BuildRequest request) throws DockerException, IOException {
+	public void build(BuildRequest request) throws DockerEngineException, IOException {
 		Assert.notNull(request, "Request must not be null");
 		this.log.start(request);
 		Image builderImage = pullBuilder(request);

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/docker/DockerApi.java

@@ -26,7 +26,8 @@
 
 import org.apache.http.client.utils.URIBuilder;
 
-import org.springframework.boot.buildpack.platform.docker.Http.Response;
+import org.springframework.boot.buildpack.platform.docker.transport.HttpTransport;
+import org.springframework.boot.buildpack.platform.docker.transport.HttpTransport.Response;
 import org.springframework.boot.buildpack.platform.docker.type.ContainerConfig;
 import org.springframework.boot.buildpack.platform.docker.type.ContainerContent;
 import org.springframework.boot.buildpack.platform.docker.type.ContainerReference;
@@ -53,7 +54,7 @@ public class DockerApi {
 
 	static final String API_VERSION = "v1.24";
 
-	private final Http http;
+	private final HttpTransport http;
 
 	private final JsonStream jsonStream;
 
@@ -67,23 +68,23 @@ public class DockerApi {
 	 * Create a new {@link DockerApi} instance.
 	 */
 	public DockerApi() {
-		this(new HttpClientHttp());
+		this(HttpTransport.create());
 	}
 
 	/**
-	 * Create a new {@link DockerApi} instance backed by a specific {@link HttpClientHttp}
+	 * Create a new {@link DockerApi} instance backed by a specific {@link HttpTransport}
 	 * implementation.
 	 * @param http the http implementation
 	 */
-	DockerApi(Http http) {
+	DockerApi(HttpTransport http) {
 		this.http = http;
 		this.jsonStream = new JsonStream(SharedObjectMapper.get());
 		this.image = new ImageApi();
 		this.container = new ContainerApi();
 		this.volume = new VolumeApi();
 	}
 
-	private Http http() {
+	private HttpTransport http() {
 		return this.http;
 	}