The test was passing previously because the preamble was already buffered. After
the change to return Scanner.Err() the final read error on the buffer was no
longer being ignored.
Signed-off-by: Daniel Nephin <dnephin@docker.com>
Redefine a better interface for remote context dependency.
Separate Dockerfile build instruction from remote context.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
