CI: update supported platforms

ci/images/full/centos-7/Dockerfile

-FROM registry.nic.cz/packaging/apkg/systemd/centos-7
-
-WORKDIR /root
-CMD ["/bin/bash"]
-
-# overcome locale issues
-RUN yum install -y glibc-common
-RUN localedef -i en_US -f UTF-8 C.UTF-8
-
-# upgrade system to latest
-RUN yum upgrade -y
-# enable EPEL
-RUN yum install -y epel-release
-# enable centos-release-scl
-RUN yum install -y centos-release-scl
-
-# packaging deps
-RUN yum install -y \
-    git \
-    rpm-build \
-    python3-setuptools \
-    python3-pip
-# basic deps
-RUN pip3 install \
-    beautifulsoup4 \
-    blessings \
-    cached-property \
-    click \
-    distro \
-    jinja2 \
-    packaging \
-    requests \
-    toml
-# install stable apkg from PyPI
-RUN python3 -m pip install apkg
-RUN apkg --version