The initial `ValidateContextDirectory` implementation fails loudly when a file
lacks read permissions in the current context. However that situation is valid
if the file is included in the `.dockerignore` patterns.
Docker-DCO-1.1-Signed-off-by: Bruno Renié <brutasse@gmail.com> (github: brutasse)
Upstream-commit: 27cca4c70cc7f0cccfda693ca7bbb2422eec3e13
Component: engine
604012d742