OOIION-1077 (partial)

Good part of the implementation for https://jira.oceanobservatories.org/tasks/browse/OOIION-1077

See https://gist.github.com/carueda/5754711 for relevant logging from the new test: ion/services/sa/observatory/test/test_platform_status.py:Test.test_platform_status_terminate_and_restart_instrument_1_1, which completes OK.

PR mainly for review at the moment.  (but it could be merged as it would be good to see how the test runs on the various buildbots).