Config updates and note for install_minimal.

I'm creating this pull request against saas, because that's where the config values below are required, however we would probably want to put this in 2.5.x since the way we install saas is by installing 2.5.x and switching the branch to saas.  When we install from 2.5.x, we'll be copying that branch's airtime.conf to /etc/airtime/conf, so by default you'd still need to manually edit the config file, which kind of defeats the purpose of this commit.

Is there any possible down side to putting these changes in 2.5.x and pulling them from there into saas and other branches?
I actually don't know what this is for (or what It means, tried googling it).  Duncan recommended adding this to the rabbitmq.ini and rabbitmq-... ini files in the airtime-saas directory.  Since those files take information from airtime.conf, I decided to put this in airtime.conf and the copy over the conf files, which makes the install process a bit easier.  I'm not sure what affect this has in any of the files it resides in.