Fix getting instance events on subsequent attempts

When the code for getting the list of events for a given instance
was moved into the InstanceEvents object, an indenting error was
introduced, which causes the get method to return None instead of
the list if the instance already has some events waiting.

This corrects that issue.

Closes-bug: #1296808
Change-Id: I099a605980dd9c2ae0659b82c633caeb8a19bbe9