Add mongo docker container OPS-2205

docker/build/mongo/Dockerfile

+FROM edxops/xenial-common:latest
+MAINTAINER edxops
+
+ADD . /edx/app/edx_ansible/edx_ansible
+COPY docker/build/mongo/ansible_overrides.yml /
+
+WORKDIR /edx/app/edx_ansible/edx_ansible/docker/plays
+
+RUN /edx/app/edx_ansible/venvs/edx_ansible/bin/ansible-playbook mongo.yml \
+    -i '127.0.0.1,' -c local \
+    -t 'install' \
+    -e@/ansible_overrides.yml
+
+WORKDIR /edx/app
+EXPOSE 27017

docker/build/mongo/ansible_overrides.yml

+{}

docker/plays/mongo.yml

+- name: Deploy MongoDB 3.2
+  hosts: all
+  become: True
+  gather_facts: True
+  roles:
+    - common_vars
+    - docker
+    - mongo_3_2