[focal] various DKMS fixes

[Andy Whitcroft]

We have a few outstanding linux/linux-restricted modules DKMS related
issues.

1) the fixes to use the librarian are incomplete for ports architectures
which are firewalled from the librarian on https.  Fix this by
introducing a new file-downloader helper which converts these URLs to
http which are permitted,

2) The Nvidia modules need to have versioned provides to allow them to
replace the relevant dkms packages,

3) Introduces signed wireguard modules.  This is included in this series
as it is dependant on the versioned provides support above.

There is a cranky-fix update coming which will help propogate the
necessary packaging changes to derivatices.

These are presented as two pull requests, the first for focal:linux-5.4
and the second for focal:linux-restricted-modulees-5.4.

Proposing for focal for fuller testing.

-apw

===
The following changes since commit 1032f4a665a449853aea4677758c7d4c7d5276e4:

  UBUNTU: [Packaging] Fix ubuntu-regression-suite python dependency for hwe kernel (2020-01-19 19:59:07 -0600)

are available in the Git repository at:

  https://git.launchpad.net/~apw/ubuntu/+source/linux/+git/focal dkms-build--various-fixes

for you to fetch changes up to 97b327549ebe9a96648b54c172e129230eea7bd7:

  UBUNTU: [Config] wireguard -- enable on all architectures (2020-01-29 14:12:04 +0000)

----------------------------------------------------------------
  * Build and ship a signed wireguard.ko (LP: #1861284)
    - [Packaging] wireguard -- add support for building signed .ko
    - [Config] wireguard -- enable on all architectures

  * installing linux-modules-nvidia does not remove nvidia-dkms, and the kernel
    prioritizes the wrong version of the module from disk (LP: #1856414)
    - [packaging] dkms-build -- include versioned provides
    - [Packaging] dkms -- add Provides: specifiers for existing zfs/nvidia/vbox

  * dkms artifacts may expire from the pool (LP: #1850958)
    - [Packaging] autoreconstruct -- manage executable debian files
    - [packaging] handle downloads from the librarian better

===
The following changes since commit 9e67b1ae44efdf982c731de83c0645c7154d67ed:

  UBUNTU: Ubuntu-5.4-5.4.0-12.15 (2020-01-21 14:55:20 +0100)

are available in the Git repository at:

  https://git.launchpad.net/~apw/ubuntu/+source/linux-restricted-modules/+git/focal dkms-build--various-fixes

for you to fetch changes up to 8f6189a0e8a18b6702c3f7a1755468e17b3561da:

  UBUNTU: [Packaging] resync dkms-build and family (2020-01-29 14:21:22 +0000)

----------------------------------------------------------------
  * Packaging resync (LP: #1786013)
    - [Packaging] resync dkms-build and family

  * Miscellaneous Ubuntu changes
    - [Packaging] fix-filenames -- build during build phase
    - [Packaging] dkms -- add Provides: specifiers for existing nvidia packages