TT#44814 Fix perms on /etc/mysql/grants.yml

The .postbuild config has been removed from /etc/mysql/grants.yml
as a result the file is installed with 0400 perms.
Fix the test accordingly.

P.S. Makefile contains 0600, but ngcpcfg removes write for everyone on apply.

Change-Id: I16830fc14c262261dc5a4c20c47bda7f296d95bc

templates/130_filesys-ngcp.yaml.tt2

@@ -146,7 +146,7 @@ file:
 
   /etc/mysql/grants.yml:
     exists: true
-    mode: "0600"
+    mode: "0400"
     owner: root
     group: root
     filetype: file