[SRU bionic/linux-gcp xenial/linux-gcp] LP#1782557 -- switch to signed kernels

[Andy Whitcroft]

We have been requested to provide signed kernels for the GCP cloud.
Therefore we need to switch on EFI signing for this kernel and
create the required additional -signed package for it.

Following this email are patches for bionic/linux-gcp and
xenial/linux-gcp which enable generation of the associated signing
uploads to trigger signing.

We also require a new signing package.  As this is an all new package in
an all new repository I have pushed the bionic/linux-signed-gcp and
xenial/linux-signed-gcp to the official respositories.  These can be
found in launchpad as below:

    lp:~canonical-kernel/ubuntu/linux-signed-gcp/+git/bionic
    lp:~canonical-kernel/ubuntu/linux-signed-gcp/+git/xenial

For each there is master tip with a ficticious initial upload at
the version in -updates, with associated tagging to let the internal
update scripts to work on first update in the new SRU cycle.

Proposing for SRU to bionic and xenial.

-apw