For some reason, docker pull seems to leave a non-daemon thread behind, prevent the jvm from shutting down right away
But not when running it as a junit test
mvn compile && time mvn exec:java -Dexec.mainClass="com.richodemus.test.docker.bug.DockerImagePuller"
- run DockerImagePuller.main(), the image will be downloaded but the program will not terminate until a minute later
- run DockerImagePullerTest.works(), the image will be downloaded and the test will finish