By default the Docker client's build command will set the --rm option to true so that intermediate containers are cleaned up once the build completes. This is useful since it avoids cluttering up the list of stopped containers. I noticed this after I switched gradle-docker to use the API instead of the command line client, so I wanted to bring the two in line. The API supports this option, so I added it to BuildImgCmd.java with a default setting of true.

The build API also supports a -q option which can be used to suppress output. By default this is false. This option was added as well.