ncm-mysql: option for support of other mysql servicenames

option `servicename` added, which make other servicenames possible, and disables `chkconfig` for EL7
it's desirable to have it implemented in same modularity as the rest of `CAF::Service`, but the problem remains that if this would be general practise, we'd have more then one way to do the same (or the opposite), so very hard to garantee something is done as we'd expect.
imho `chkconfig` does not belong in a component, but if this is legacy behaviour, maybe just keep the old behaviour. and assume that `chkconfig` is correct or add another boolean to skip the chkconfig part here.