Revert "ceph-validate: use root device from ansible_mounts"

This reverts commit b1542fd.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>

roles/ceph-validate/tasks/check_devices.yml

@@ -1,7 +1,17 @@
 ---
+- name: find device used for operating system
+  command: findmnt -v -n -T / -o SOURCE
+  changed_when: false
+  register: root_device
+
+- name: resolve root_device
+  command: "readlink -f {{ root_device.stdout }}"
+  changed_when: false
+  register: _root_device
+
 - name: set_fact root_device
   set_fact:
-    root_device: "{{ ansible_facts['mounts'] | selectattr('mount', 'match', '^/$') | map(attribute='device') | first }}"
+    root_device: "{{ _root_device.stdout }}"
 
 - name: lvm_volumes variable's tasks related
   when: