Merge pull request #4107 from edx/nadeem/OPS-2398

Playbook to update or create a new install of mongo_mms

playbooks/edx-east/mongo_mms.yml

+- name: Deploy mongo_mms instance
+  hosts: all
+  become: True
+  gather_facts: True
+  vars:
+    serial_count: 1
+  serial: "{{ serial_count }}"
+  roles:
+    - aws
+    - mongo_mms
+    - role: newrelic
+      when: COMMON_ENABLE_NEWRELIC
+    - role: datadog
+      when: COMMON_ENABLE_DATADOG