UBUNTU: [packaging] handle downloads from the librarian better

When downloading from the librarian on a buildd (the common case) we cannot
use https to obtain those files (we are only guarenteed access to the
librarian on http from the DCs).  Add a new downloader which understands
this and fixed up downloads triggered via librariant +files redirects.
Switch us from wget to curl for downloads under the hood so update the
build-depends.

BugLink: http://bugs.launchpad.net/bugs/1850958
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>

debian.oem/control.stub.in

@@ -35,7 +35,7 @@ Build-Depends:
  uuid-dev <!stage1>,
  libnuma-dev [amd64 arm64 ppc64el s390x] <!stage1>,
  dkms <!stage1>,
- wget <!stage1>,
+ curl <!stage1>,
  lz4 [amd64 s390x] <!stage1>,
 Build-Depends-Indep:
  xmlto <!stage1>,