Plugin does not work with custom Docker credHelpers.

[tsolakp]

I need to push docker images into Amazon EC2 Container repo and since the plugin does not support it I am using "credHelpers" in config.json along with https://github.com/awslabs/amazon-ecr-credential-helper.
Command line "docker push imagename" works without requiring login and any authentication errors. But when using with plugin I am getting this exception:

org.apache.maven.plugin.MojoExecutionException: Could not push image at com.spotify.plugin.dockerfile.PushMojo.execute(PushMojo.java:90) at com.spotify.plugin.dockerfile.AbstractDockerMojo.tryExecute(AbstractDockerMojo.java:227) at com.spotify.plugin.dockerfile.AbstractDockerMojo.execute(AbstractDockerMojo.java:216) at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134) at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:207) at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153) at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145) at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116) at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80) at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51) at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128) at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307) at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193) at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106) at org.apache.maven.cli.MavenCli.execute(MavenCli.java:863) at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288) at org.apache.maven.cli.MavenCli.main(MavenCli.java:199) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289) at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229) at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415) at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356) Caused by: com.spotify.docker.client.exceptions.DockerException: no basic auth credentials at com.spotify.plugin.dockerfile.LoggingProgressHandler.handleError(LoggingProgressHandler.java:105) at com.spotify.plugin.dockerfile.LoggingProgressHandler.progress(LoggingProgressHandler.java:63) at com.spotify.docker.client.ProgressStream.tail(ProgressStream.java:74) at com.spotify.docker.client.DefaultDockerClient.push(DefaultDockerClient.java:1291) at com.spotify.docker.client.DefaultDockerClient.push(DefaultDockerClient.java:1271) at com.spotify.plugin.dockerfile.PushMojo.execute(PushMojo.java:88)

Seems like the plugin is not including "credHelpers" when serializing config.json.

[mattnworb]

Thanks for the report. See #24 which already covers this.