linux-meta-gke needs to provide metapackages in non-LTS releases to ensure smooth upgrades between releases

[Steve Langasek]

The linux-gke kernel is only maintained in xenial, which is by design. However, if someone installs an instance with xenial and then dist-upgrades it to yakkety, they will be islanded on whatever release of linux-gke was current at time of upgrade.

The linux-meta-gke package needs to track the generic linux package in non-LTS releases. This will not give the users all of the gke-specific goodness, but will ensure they have a clean upgrade path, both between non LTS releases and for LTS->LTS upgrades.

[Steve Langasek (vorlon)]

This would *also* allow us to use custom kernels for non-LTS cloud images that are produced, so that any users who install a non-LTS image, and then upgrade it to 18.04, will get the intended custom kernel for that environment.

[Andy Whitcroft (apw)]

We should add these as transitionals on linux-meta to simplify maintenance. The version of the base kernel should exceed that in xenial.

[Andy Whitcroft (apw)]

This should apply equally to any X only customkernel of this type.