Provide start argument to run dev mode

For years now, I've been compiling Openfire, start it from source, go through the set up to configure Openfire with a hostname-based XMPP domain, embedded database and predictable admin account, then do some testing.

Although it's easy enough to do, it would be so much easier to just have a flag that'd automate this.

Dan Caseley added a 'demoboot' openfire.xml file not to long ago, which basically provides this feature. Adding that to the start script would probably get us 90% there.