[TESTS] Be less strict about breaker child limit

Failing a parent breaker check is eventually consistent, so the test
could fail the parent limit, throw an exception, and before being
adjusted back down, increment more and throw a circuit breaking
exception on the child. This increases the child's limit, to ensure
we're only testing the parent limit.

It adds an additional assert to ensure that the breaker total is
correctly re-adjusted when the parent breaker has been tripped.