remount: PB to remount read-only filesystems

Many hosts have a read-only root filesystem, as well as some other
read-only paths that need to be remounted before configuration changes
can be made. The `remount.yml` playbook can be used to remount select
filesystems as either read-write or read-only (the default). It is
intended to be used before and after other playbooks, to ensure the
filesystems are in the correct state.

remount.yml

@@ -0,0 +1,20 @@
+- hosts: all
+  gather_facts: true
+  vars:
+    remount_state: ro
+    remount_fs:
+    - /
+    - /usr
+    - /opt
+  tasks:
+  - name: remount filesystems
+    command:
+      mount -oremount,{{ remount_state }} {{ item }}
+      warn=false
+    with_items: >-
+      {{
+      ansible_mounts
+         | selectattr('mount', 'in', remount_fs)
+         | map(attribute='mount')
+         | list
+      }}