Create start / stop integration tests...

[choksi81]

We should have some integration tests that start / stop seattle a bunch of times. I did this today and found two separate bugs (#599 and #600)!

[aaaaalbert]

There are multiple things that a test suite for this should test:

• The OS-specific start/stop scripts/batch files, https://github.com/SeattleTestbed/installer-packaging/tree/master/script_wrappers
• https://github.com/SeattleTestbed/installer-packaging/blob/master/all-platforms/stop_all_seattle_processes.py
• Probably also the nodemanager directly

All of these are interesting because of possible race conditions in sending a termination signal vs checking that the process really has terminated. (@XuefengHuang, IIRC starting/stopping Seattle on OpenWrt produces an error message relatively often, although the nodemanager eventually starts/stops.)