In 566f41b598b350c2e92df69a4b8392863ae47faf, we added a check to ensure
that we avoid resolving http URLs for Dockerfile. However, we have
another circumstance we should not resolve the path in - if the context
is a remote context, the dockerfile is resolved in that context (see
build.go#LoadInputs for more information).
Therefore, we should only resolve the dockerfile to a local directory if
the context is also resolved to a local directory.
Signed-off-by: Justin Chadwell <me@jedevc.com>