Hard coded /kaniko directory from #2863 should be parameterized for usage w/ --kaniko-dir, etc.

[aaron-prindle]

Currently the fix made in #2863 uses a hardcoded /kaniko directory but this can be changed by the user with the KANIKO_DIR env var or --kaniko-dir flag

NOTE: we might want to always have /kaniko skipped but additionally Skip the --kaniko-dir var as the /Kaniko dir in the image (vs just using the parameter). This is because the /kaniko dir in the image is pre-populated with files (Kaniko binary, etc.) that likely aren't desired for users to have in their image(s)