automation: Rework archlinux container

Base image "archlinux/base" isn't available anymore,
    https://lists.archlinux.org/pipermail/arch-dev-public/2020-November/030181.html

But instead of switching to archlinux/archlinux, we will use the
official image from Docker. Main difference is that the first one is
updated daily while the second is updated weekly.

Also, as we will install the packages from "base-devel" anyway, switch
to the "base-devel" tag.

"dev86" package is now available from the main repo, no need for
multilib repo anymore.

It is recommended to initialise local signing key used by pacman, so
let's do that.

Replace "markdown" by "discount" as the former isn't available anymore
and has been replaced by the later.

Also, clean pacman's cache.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

automation/build/archlinux/current.dockerfile

@@ -1,16 +1,15 @@
-FROM archlinux/base
+FROM archlinux:base-devel
 LABEL maintainer.name="The Xen Project" \
       maintainer.email="xen-devel@lists.xenproject.org"
 
-# Enable multilib repo, for dev86 package
-RUN echo $'[multilib]\nInclude = /etc/pacman.d/mirrorlist' >> /etc/pacman.conf
+RUN pacman-key --init
 
 RUN pacman -S --refresh --sysupgrade --noconfirm --noprogressbar --needed \
-        base-devel \
         bin86 \
         bridge-utils \
         bzip2 \
         dev86 \
+        discount \
         dtc \
         e2fsprogs \
         ghostscript \
@@ -29,7 +28,6 @@ RUN pacman -S --refresh --sysupgrade --noconfirm --noprogressbar --needed \
         libnl \
         libpng \
         libseccomp \
-        markdown \
         net-tools \
         nss \
         perl \
@@ -46,7 +44,8 @@ RUN pacman -S --refresh --sysupgrade --noconfirm --noprogressbar --needed \
         wget \
         xz \
         yajl \
-        zlib
+        zlib \
+    && yes | pacman -S --clean --clean
 
 ENV PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl