When we execute multistage builds, we store the fs of each intermediate
stage at /kaniko/<stage number> if it's used later in the build. This
created a bug when extracting hardlinks, because we weren't appending
the new directory to the link path.
So, if `/tmp/file1` and `/tmp/file2` were hardlinked, kaniko was trying
to link `/kaniko/0/tmp/file1` to `/tmp/file2` instead of
`/kaniko/0/tmp/file2`. This change will append the correct directory to
the link, and fixes#437#362#352#342.
Extracting the layers of the filesystem in order will make it easier to
extract cached layers and deal with hardlinks.
This PR implements extracting in order and adds an integration tests to
make sure hardlinks are extracted properly.
It also fixes two bugs I found when extracting symlinks:
1. We'd get a "file exists" error when trying to symlink to an existing
file with a whiteout later in the layer tarball
2. We'd get a "file exists" error when trying to create a symlink from a
file that was created in a prior layer (perhaps as a regular file or as
a symlink pointing to someting else)
To fix both of these, we resolve all symlinks in a layer at the end. I
also added logic to delete any existing paths before creating the
symlink.
Priya Wadhwa