Set Travis file to only run test_brokers
Set Travis file to only run test_brokers

- Set Travis file to only run test_brokers (and exclude crypto and ssm
  tests) as they haven't been tweaked to work with Travis yet.

apel/ssm,stfc/ssm,stfc/ssm,tofu-rocketry/ssm,apel/ssm,tofu-rocketry/ssm