* Again in ubuntu-server builds, configure LAYERFS_PATH in the kernel layer
and ensure the initrd is freshly regenerated in that layer. LAYERFS_PATH
was being set to the layer below the kernel layer, which meant that the
live session did not get access to all the modules in the case that the
kernel had not been installed in the base layer, which in turn means that
installs fail. (LP: #2100148)
* While we're at it, delete any initrd from any other layer than a kernel
layer, as they just waste space on the ISO.
