remount-usr: use findmnt to find if usr is a readonly partition

CHANGELOG.md

@@ -15,6 +15,7 @@ The **patch** part changes is incremented if multiple releases happen the same m
 ### Changed
 
 * evolinux-base: many improvements for backup-server-state script
+* remount-usr: use findmnt to find if usr is a readonly partition
 
 ### Fixed
 

remount-usr/tasks/main.yml

@@ -1,10 +1,10 @@
 ---
+# findmnt returns 0 on hit, 1 on miss
+# If the return code is higher than 1, it's a blocking failure
 - name: "check if /usr is a read-only partition"
-  command: 'grep -E " /usr.*ro" /proc/mounts'
-  args:
-    warn: no
+  command: 'findmnt /usr --noheadings --options ro'
   changed_when: False
-  failed_when: False
+  failed_when: usr_partition.rc > 1
   check_mode: no
   register: usr_partition