Cleanup log location config in sysconfig/init scripts

Set log_file default to client.log (nobody would log in stdout when running chef-client as a service IMO).

Remove all references to LOG_LOCATION in sysconfig/init scripts since client.rb config file will set it.

It should make configuration clearer and allow users to set log_location in client.d/something.rb without having to fight againts init scripts.

This can replaces #163 
Might be good to nuke this comment, as well.