Fix docker image build - add python3

Building the docker image does not work anymore, see #2601

Add python3 to the list of available packages

cd docker
docker build --build-arg BK_VERSION=4.12.1 -t testbk .

Fixes #2601

Reviewers: Andrey Yegorov <None>

This closes #2609 from eolivelli/fix/docker-image-python3

(cherry picked from commit 503e0c29b5acd99f0ec52449f412cb3dbeb7ae90)
Signed-off-by: Andrey Yegorov <andrey.yegorov@datastax.com>
diff --git a/docker/Dockerfile b/docker/Dockerfile
index eac6a58..26c14a7 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -33,7 +33,7 @@
 # Download Apache Bookkeeper, untar and clean up
 RUN set -x \
     && adduser "${BK_USER}" \
-    && yum install -y java-11-openjdk-devel wget bash python sudo\
+    && yum install -y java-11-openjdk-devel wget bash python3 sudo\
     && mkdir -pv /opt \
     && cd /opt \
     && wget -q "${DISTRO_URL}" \
@@ -47,7 +47,8 @@
     && mv bookkeeper-server-${BK_VERSION}/ /opt/bookkeeper/ \
     && rm -rf "$DISTRO_NAME.tar.gz" "$DISTRO_NAME.tar.gz.asc" "$DISTRO_NAME.tar.gz.sha512" \
     # install zookeeper shell
-    && wget -q https://bootstrap.pypa.io/get-pip.py \
+    && wget -q https://bootstrap.pypa.io/2.7/get-pip.py \
+    && python --version \
     && python get-pip.py \
     && pip install zk-shell \
     && rm -rf get-pip.py \