Allow test processes to shutdown gracefully
Allow test processes to shutdown gracefully

- We were performing a kill -9 which cannot be caught
- This caused frequent test failures on our Concourse linux workers
- Test failures are less frequent, but some flakiness remains

[#128245705]

cloudfoundry-incubator/switchboard,cloudfoundry-incubator/switchboard,cloudfoundry-incubator/switchboard,cloudfoundry-incubator/switchboard