TT#12307 mysql user on stretch uses /nonexistent as its home

On Debian/stretch we get /nonexistent as the home
for user mysql, while on Debian/jessie it's /var/lib/mysql.

Backported to mr4.5 as systems installed on 2.8 and
upgraded to mr3.8 and then to mr4.5 has '/nonexistent'
due to Percona DB is being used on 2.8

Change-Id: I87d6db988c5d973d5ef814a89e658080e0bd7e50
(cherry picked from commit 9c2db0284a)

ce/05_system_users.yaml.tt2

@@ -79,7 +79,10 @@ user:
     exists: true
     groups:
       - mysql
-    home: "/nonexistent"
+    home:
+      or:
+      - "/var/lib/mysql"
+      - "/nonexistent"
 
   nobody:
     exists: true