Support pegleg to run on opensuse leap15 image

Add DISTRO parameter to support multiple distros
Add Dockerfile for opensuse to build leap 15 image.

Change-Id: I7a529476937494e042a4801117489325aa6621c7

images/pegleg/Dockerfile.opensuse_15

@@ -0,0 +1,46 @@
+ARG FROM=opensuse/leap:15.0
+FROM ${FROM}
+ARG CFSSLURL=https://pkg.cfssl.org/R1.2/cfssl_linux-amd64
+
+LABEL org.opencontainers.image.authors='airship-discuss@lists.airshipit.org, irc://#airshipit@freenode'
+LABEL org.opencontainers.image.url='https://airshipit.org'
+LABEL org.opencontainers.image.documentation='https://airship-pegleg.readthedocs.org'
+LABEL org.opencontainers.image.source='https://opendev.org/airship/pegleg'
+LABEL org.opencontainers.image.vendor='The Airship Authors'
+LABEL org.opencontainers.image.licenses='Apache-2.0'
+
+ENV LANG=C.UTF-8
+ENV LC_ALL=C.UTF-8
+
+RUN set -x && \
+    zypper up -y && \
+    zypper --non-interactive install \
+       git-core \
+       which \
+       gcc \
+       curl \
+       python3-devel \
+       python3-setuptools \
+       python3-dbm \
+       python3-pip && \
+       pip install --upgrade pip && \
+       zypper clean -a && \
+       rm -rf \
+         /tmp/* \
+         /var/tmp/* \
+         /var/log/* \
+         /usr/share/man \
+         /usr/share/doc \
+         /usr/share/doc-base
+
+VOLUME /var/pegleg
+WORKDIR /var/pegleg
+
+COPY requirements.txt /opt/pegleg/requirements.txt
+RUN pip3 install --no-cache-dir -r /opt/pegleg/requirements.txt
+
+COPY tools/install-cfssl.sh /opt/pegleg/tools/install-cfssl.sh
+RUN /opt/pegleg/tools/install-cfssl.sh ${CFSSLURL}
+
+COPY . /opt/pegleg
+RUN pip3 install -e /opt/pegleg