* Write parent directories to tar before whiteout files
Fixes#1149
The OCI image spec does not specify this order but it's a good idea and Docker
does the same.
When manually comparing layers created by Docker and Kaniko there are still
some differences (that container-diff does not show):
* Kaniko adds / to layers
* For `mkdir /test`, docker adds `/test` and an opaque whiteout file
`/test/.wh..wh..opq`. Kaniko only adds `/test/` (and /).
* snapshot_test: cleanup
Fix typos and use listFilesInTar() where possible
bc46c24707