Correctly quote build args to support multiline values
Correctly quote build args to support multiline values

This change properly escapes multiline build arg values when calling `docker build`.

Fixes #158, Fixes #79

Signed-off-by: Lyle Franklin <31e283733c7a4b3b6cb03b95ab535671c2112bbe@pivotal.io>

concourse/docker-image-resource,concourse/docker-image-resource