I improved handling of the .dockerignore file by:
1. Using docker's parser to parse the .dockerignore and using their
helper functions to determine if a file should be deleted
2. Copying the Dockerfile we are building to /kaniko/Dockerfile so that
if the Dockerfile is specified in .dockerignore it won't be deleted, and
if it is specified in the .dockerignore it won't end up in the final
image
3. I also improved the integration test to create a temp directory with
files to ignore, and updated the .dockerignore to include exclusions (!)
55e6157000