Refactor Actions to use UUID instead of Sequence

First step in process of consolidating Actions and ActionResults.
Also part of exposing UUID to end clients rather than the Sequence
id that was not guaranteed to reflect order of enqueing.

A couple of other tweaks to avoid calling code that might panic in
non testing code.
address review feedback
Fix test
Merge pull request #1140 from johnweldon/1-action-sequence-to-uuid

Refactor Actions to use UUID instead of Sequence

First step in process of consolidating Actions and ActionResults.
Also part of exposing UUID to end clients rather than the Sequence
id that was not guaranteed to reflect order of enqueing.

A couple of other tweaks to avoid calling code that might panic in
non testing code.