use correct logger while migration

[tsechingho]

It should use $LOG to assign logger, since the CASServer::Model::Ticket module is no more has logger method/variable.

It also needs to require 'casserver/authenticators/base' to make migrate work.

I also fix the rake description.

[mitfik]

Hi, thanks for contribution

Actually I do not see any reason why we would like to keep that task but maybe there is some black magic behind it. But anyway, when you are running the server, migration will be done in init_database so it means that there is no need to run that task before.

But since we already have it we will maintain that code of course there is just question if we need to set the $LOG here as AR will use own logger for that purpose.

I prepared a new pull request (#218) based on your code which I think make much more sens in that case. Take a look and give some feedback if this will do the job.