ci: ensure pigz is installed in the CI containers

pigz speeds up things considerably. Although pigz is already installed
by default, explicitely adding it makes sure, it will not disappear
unnoticed.

test/container/Dockerfile-Fedora-33

@@ -10,6 +10,7 @@ RUN echo 'export DRACUT_NO_XATTR=1 KVERSION=$(cd /lib/modules; ls -1 | tail -1)'
 # Install needed packages for the dracut CI container
 RUN dnf -y install --setopt=install_weak_deps=False \
     dash \
+    pigz \
     asciidoc \
     mdadm \
     lvm2 \

test/container/Dockerfile-Fedora-34

@@ -10,6 +10,7 @@ RUN echo 'export DRACUT_NO_XATTR=1 KVERSION=$(cd /lib/modules; ls -1 | tail -1)'
 # Install needed packages for the dracut CI container
 RUN dnf -y install --setopt=install_weak_deps=False \
     dash \
+    pigz \
     asciidoc \
     mdadm \
     lvm2 \

test/container/Dockerfile-Fedora-latest

@@ -10,6 +10,7 @@ RUN echo 'export DRACUT_NO_XATTR=1 KVERSION=$(cd /lib/modules; ls -1 | tail -1)'
 # Install needed packages for the dracut CI container
 RUN dnf -y install --setopt=install_weak_deps=False \
     dash \
+    pigz \
     asciidoc \
     mdadm \
     lvm2 \

test/container/Dockerfile-OpenSuse-latest

@@ -13,7 +13,7 @@ RUN dnf -y install --setopt=install_weak_deps=False \
     strace libkmod-devel gcc bzip2 xz tar wget rpm-build make git bash-completion \
     sudo kernel dhcp-client qemu-kvm /usr/bin/qemu-system-$(uname -m) e2fsprogs \
     tcpdump iproute iputils kbd NetworkManager btrfsprogs tgt dbus-broker \
-    iscsiuio open-iscsi which ShellCheck procps \
+    iscsiuio open-iscsi which ShellCheck procps pigz \
     && dnf -y update && dnf clean all
 
 RUN shfmt_version=3.2.4; wget "https://github.com/mvdan/sh/releases/download/v${shfmt_version}/shfmt_v${shfmt_version}_linux_amd64" -O /usr/local/bin/shfmt \