Added cassandra together with Wim

roles/cassandra/tasks/main.yml

@@ -0,0 +1,16 @@
+# Install a docker based cassandra cluster.
+---
+- include: ../common/tasks/docker.yml
+- name: install service file.
+  template:
+    src: templates/cassandra.service
+    dest: /etc/systemd/system/cassandra.service
+    mode: 644
+    owner: root
+    group: root
+- name: install service file
+  command: systemctl daemon-reload
+- name: make sure service is started
+  systemd:
+    name: cassandra.service
+    state: started