Continued Resource::Manger cleanup (JIRA RIPD-372)

 - Incorporates review comments from previous commit.
 - Increases Resource::Manager unit test coverage: verify a dropped consumer is blocked for a while.

Let me clarify, I'm not against documentation for private functions but they should go in the definition rather than in the synopsis in the header. And they should not be Javadoc/Doxygen comments (because these interfaces can change, and they are private).