Check for .dockerignore specifically
Check for .dockerignore specifically

When generating the list of exclusions to process .dockerignore
contents, don't include .dockerignore if we don't have a .dockerignore
file in the context directory.  That way, if the file doesn't exist, and
the caller didn't pass in any patterns, we get no patterns instead of
just one ".dockerignore" pattern, and we can hit the faster copy path.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

Closes: #2072
Approved by: giuseppe

rhatdan/buildah,nalind/buildah-1,nalind/buildah-1,rhatdan/buildah,TomSweeneyRedHat/buildah,nalind/buildah,nalind/buildah-1,TomSweeneyRedHat/buildah,TomSweeneyRedHat/buildah,projectatomic/buildah,nalind/buildah,projectatomic/buildah,projectatomic/buildah,rhatdan/buildah