Added mdadm module that will create, stop and remove Linux software RAID devices.

This is a module that utilizes mdadm to create, stop and remove Linux software RAID devices.

```yaml
  tasks:
    - name: Create mdadm raid device
      mdadm: >
        level=0
        chunk=256
        metadata="1.0"
        devices="/dev/xvdb,/dev/xvdc"
        device_name="/dev/md0"
        state=present
      tags:
      - present
    - name: Stop mdadm raid device
      mdadm: >
        device_name="/dev/md0"
        state=stopped
      tags:
      - stop
    - name: Removing mdadm raid device
      mdadm: >
        device_name="/dev/md0"
        state=absent
      tags:
      - remove
```