Add test job with multirate GBODE

[casella]

@adrpo I'd like to run the library testsuite with multirate GBODE. There is no need to do it on a daily basis, it could be a job that is run manually every now and then.

The setup is very similar to the gbode job which is already in place, you just need to add -gbratio=0.05 to the simulation flags.

Thanks!