Use Environment Variables instead of CHANGEME(USERNAME)'s throughout the code

[jsamuel1]

Rather than people search/replacing through the code, if instead there were a standard set of Environment variables that people should set (eg. $(SCOUT_HOME) and $(SCOUT_MOUNTDIR) ), then peoples source directory could remain untainted as updated are made to the code.

If a particular config file can't read environment variables, then an install script could generate the config file from the environment.

[trumankain]

Totally right. I'll be doing this shortly unless there's a PR submitted beforehand.