[OC-11712] Allow Group to Read Logfiles

* Change log_dir perms to 0750 all over
* Set perms for postgresql explictly
* Change perms to single quotes
Adjust group usage for log dirs

* Add an OmnibusHelper method to provide an owner and group hash
* Reference owner and group for log dirs in recipes where only owner is found
* Fix other recipe locations referencing node['private_chef']['user']['username'] directly
Merge branch 'sh/fix-logdir-perms-master-take2'
Respect the max shared mem lists for postgresql.  Issue #597