test suite: gdr-viagit, gdr-newupstream: do not auto-import t-setup-gnupg.

test suite: gdr-viagit, gdr-newupstream: do not auto-import t-setup-gnupg.

We provide a new mechanism for individual tests to disable the
automatic t-setup-import of gnupg.

We need to add this to all the other setup/ that these import, too.
gdr-convert-gbp is particularly awkward because it wants gnupg if
$ifarchive isn't `:'.  There we arrange to suppress its automatic
inclusion, but add it again by hand if appropriate.

This fixes these two tests in chroots without gnupg.

Closes:#902559.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>