tests/docker: add CentOS 8 Dockerfile

Which is currenly missing, and will be referenced later in the
contributed CI playbooks.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200312193616.438922-2-crosa@redhat.com>
Signed-off-by: Cleber Rosa <crosa@redhat.com>

tests/docker/dockerfiles/centos8.docker

+FROM centos:8.1.1911
+
+RUN dnf -y update
+ENV PACKAGES \
+    SDL-devel \
+    bison \
+    bzip2 \
+    bzip2-devel \
+    dbus-daemon \
+    flex \
+    gcc \
+    gcc-c++ \
+    gettext \
+    git \
+    glib2-devel \
+    libaio-devel \
+    libepoxy-devel \
+    lzo-devel \
+    make \
+    mesa-libEGL-devel \
+    nettle-devel \
+    perl-Test-Harness \
+    pixman-devel \
+    python36 \
+    rdma-core-devel \
+    spice-glib-devel \
+    spice-server \
+    tar \
+    zlib-devel
+
+RUN dnf install -y $PACKAGES
+RUN rpm -q $PACKAGES | sort > /packages.txt