XD-1172: restore previous cmd line lib

Went with an initializer that will override the default boot options. Way nicer in the main class code IMO than my previous PR.

Also, kept the ugly CAPITALS in the options getters. The net effect is that if you were to put eg 
```
XD_TRANSPORT: garbage
```
in application.yml, this will be caught.

We *can* go from getXD_TRANSPORT() to getTransport(), the only thing we'd lose is that ability to catch a mistake in application.yml