Improve Security by making SASL password file 600

[dohsimpson]

I noticed that the permissions of the SASL files are 644 by default in the VMs:

-rw-r--r--    1 root     root           101 Dec 22 16:32 sasl_passwd
-rw-r--r--    1 root     root         12288 Dec 22 16:32 sasl_passwd.lmdb

Best to keep them 600 as discussed in the doc for security best practice