Default PATH different to docker-build's

[djuarezg]

Actual behavior
On https://github.com/GoogleContainerTools/kaniko/blob/master/pkg/constants/constants.go#L75 there is a default PATH for scratch, which seems like an attempt to replicate docker-build default PATH as in https://github.com/moby/moby/blob/8e610b2b55bfd1bfa9436ab110d311f5e8a74dcb/pkg/system/path.go#L12

The problem is that this causes a change of behaviour in Kaniko. While using an image without PATH as FROM adds a default PATH in docker-build, Kaniko does not, probably because of #89

Expected behavior

A kaniko build with a base image without PATH should add the same default PATH as with docker-build.

[djuarezg]

Any update?