Add Dockerfile for building testing image

There are two images because it's hard to install both Python 2
and Python 3 packages (e.g. libcomps) in latest fedora release.

JIRA: RHELCMP-4580
Signed-off-by: Haibo Lin <hlin@redhat.com>

tests/Dockerfile-test

@@ -0,0 +1,22 @@
+FROM fedora:33
+LABEL \
+    name="Pungi test" \
+    description="Run tests using tox with Python 3" \
+    vendor="Pungi developers" \
+    license="MIT"
+
+RUN dnf -y update && dnf -y install \
+        findutils \
+        git \
+        koji \
+        make \
+        python3-createrepo_c \
+        python3-tox \
+        python3-urlgrabber \
+    && dnf clean all
+
+WORKDIR /src
+
+COPY . .
+
+CMD ["tox", "-e", "flake8,black,py3"]

tests/Dockerfile-test-py2

@@ -0,0 +1,25 @@
+FROM centos:7
+LABEL \
+    name="Pungi test" \
+    description="Run tests using tox with Python 2" \
+    vendor="Pungi developers" \
+    license="MIT"
+
+RUN yum -y update && yum -y install \
+        git \
+        make \
+        python3 \
+        python-gssapi \
+        python-libcomps \
+        python-createrepo_c \
+        pykickstart \
+    && yum clean all
+
+# python-tox in yum repo is too old, let's install latest version
+RUN pip3 install tox
+
+WORKDIR /src
+
+COPY . .
+
+CMD ["tox", "-e", "py27"]