Update _loadConfigs to support environment var replacement.
Update _loadConfigs to support environment var replacement.

Configuration items specified as a string, which start with
"process.env." will be automatically replace with the matching
environment variable's value.

RobotSnacks/stout-server,JoshuaToenyes/stout-server,RobotSnacks/stout-server,JoshuaToenyes/stout-server