Chef Server does not check for necessary permissions on /var/log

[marcparadise]

Some customers set /var/log 's mode to 0700, which breaks Chef Server 12.3.1+ initial reconfigure.

/var/log/opscode is either not present or unwritable even if present and the reconfigure fails.

Let's add a preflight check for permissions that verifies /var/log as 0755 and provides a meaningful message with remediation steps to the customer if permissions are not sufficient to permit complete a successful reconfigure.

The original PR (#695 ) changed the directory permissions as part of reconfigure, but this introduces a potential issue where installing Chef Server has an unexpected side effect (changing system directory permissions level) that may run contrary to local security policies.