This change deflakes TestTaskTemplateManager_BlockedEvents test, because
it is expecting a number of events without accounting for transitional
state.

The test TestTaskTemplateManager_BlockedEvents attempts to ensure that a
template rendering emits blocked events for missing template ksys.

It works by setting a template that requires keys 0,1,2,3,4 and then
eventually sets keys 0,1,2,3 and ensures that we get a final event indicating
that keys 3 and 4 are still missing.

The test waits to get a blocked event for the final state, but it can
fail if receives a blocked event for a transitional state (e.g. one
reporting 2,3,4,5 are missing).

This fixes the test by ensuring that it waits until the final message
before assertion.

Also, it clarifies the intent of the test with stricter assertions and
additional comments.