Adds out of band retrieval and bugfix for replay.

- Adds out of band retrieve classmethod.
- Moves coverage closing to a finally block in a try except, very
  important.
Merge pull request #444 from lukecampbell/oob_retrieval

Adds out of band retrieval and bugfix for replay.
Attempt to fix coi combined coverage
Fixes cleanup in DPMS and added data product cleanup in some tests.
Fixes empty coverage registration bug in this test.
Patches some tests (EOI) to ensure correct dataset creation.
Merge pull request #454 from lukecampbell/cleanup_fixes

Fixes cleanup in DPMS and added data product cleanup in some tests.
Merge branch 'master' into fix_or_remove_skipped_tests