M101: Initial integration of mission executive with platform agent

@edwardhunter please review/merge.

Includes:
- latest changes in Bob's mission executive.
- new integration tests to exercise mission execution via platform agent, one in COMMAND state and the other in MONITORING (aka, streaming) state.

Testing:
- All related tests are completing OK locally, but have been skipped for this PR to not "interfere" with buildbots just yet.

Note: many unrelated tests are currently failing locally, and in fact on buildbot, eg:
 http://buildbot.oceanobservatories.org:8010/builders/coi_pycc/builds/2145/steps/nose%20int%20tests/logs/stdio

Let us know how you want to proceed.