[mythtv] Using a unique key instead of hostname in settings

[Tomas Edwardsson]

I have been having problems with having to reconfigure frontends because 
someone changed a hostname or domainname. Wouldn't it make more sense 
that when generating the initial config the host would generate a unique 
ID and save it onto the filesystem. It can then be the hosts unique id 
for all settings.

- Tommi