Launch Layers Not Exported Properly

[nebhale]

In some circumstances (it's regularly reproducible but not reliable) some (not all) layers that are reused are not exported properly. Given this gist, you'll see the following:

1. During the first build, layer io.pivotal.openjdk:jvmkill is created from scratch and exported.
2. During the second build, layer io.pivotal.openjdk:jvmkill metadata is restored and resused.
3. During the second build, layer io.pivotal.openjdk:jvmkill is not exported.

[nebhale]

Debug gist