UBUNTU: [Packaging] dkms -- try launchpad librarian for pool downloads

UBUNTU: [Packaging] dkms -- try launchpad librarian for pool downloads

When we build a kernel we capture the current dkms package versions.
This allows us to keep the versions syncronised in an entire SRU cycle
between the master and derivative kernels.  It also allows us to maintain
the same versions on respin.  This suffers from the issue that they may
expire from the archive pool if the dkms packages are revved.

The same packages are available in the launchpad librarian and indeed
(now) via well known names.  So when are attempting to download from the
archive pool first attempt to get the package from the primary archive
librarian first.  If this fails continue to do the pool scan as normal.
This increases the chance we will find an appropriate package regardless
of the currently published packages, whilst retaining the ability to build
in a more restricted environment (such as when we have no internet access).

BugLink: https://bugs.launchpad.net/bugs/1850958
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>