raid-array: Add PB to create md arrays

The `raid-array.yml` playbook can create Linux *md* software RAID arrays
using the `mdadm` command.  Two variables are required: `md_name` and
`raid_disks`.  The former is a string name for the array.  The latter is
an array of paths of block devices to add to the array.

raid-array.yml

@@ -0,0 +1,31 @@
+- hosts: minio-backups
+  gather_facts: true
+  tasks:
+  - name: ensure mdadm is installed
+    package:
+      name: mdadm
+      state: present
+    tags:
+    - install
+  - name: ensure usb hdd partitions are removed
+    command:
+      wipefs -fa {{ item }}
+    args:
+      removes: '{{ item }}-part1'
+    loop: '{{ raid_disks }}'
+    tags:
+    - wipefs
+  - name: ensure md raid array exists
+    command: >-
+      systemd-cat -t mdadm
+      mdadm --create --run
+      --name={{ md_name }}
+      --level=raid1
+      --raid-devices=2 
+      /dev/md/{{ md_name }}
+      {{ raid_disks | join(' ') }}
+    args:
+      creates: /dev/disk/by-id/md-name-{{ md_name }}
+    tags:
+    - mdadm
+    - mdadm-create