Add travis-lint to list of development dependencies

This ensures the gem is installed when we run our tests via Travis CI.

Change-Id: I2eef2593b89f94828a3cdf81854e305b8d13121a
Reviewed-on: http://gerrit.causes.com/45340
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Quiet additional clone output in tests

There is one test that when run in Travis displays:

    Cloning into 'test-sub'

Silence it by redirecting both standard out and error streams.

Change-Id: I64f4955d73743c34c9c4ab9e710271bf21c40c56
Reviewed-on: http://gerrit.causes.com/45341
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>