This changes the test TestBuildWithInaccessibleFilesInContext to not
add the user 'unprivilegeduser' and add it via the Dockerfile instead.
Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
This makes container and image removal in the tests run synchronously.
Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)