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.

I would have formatted it as
m_journal.warning <<
"Consumer entry " << entry <<
" dropped with balance " << balance <<
 +                " at or above drop threshold " << dropThreshold;