Make sure dlq extent quotas are honored

[venkat1109]

DLQ destinations don't need to be scaled for high throughput most of the the time and so we have different quotas for numPublisher/numConsumer extents for DLQ. However, there are two problems currently with enforcing those quotas:

(1) The publish side quotas are never enforced because of a bug
(2) The consume side allows for violation of DLQ quota when there are no regular extents to consume from. This is not OK sometimes, because DLQs can be poison pills and consuming solely from DLQs could potentially stall a consumer group. The fix will be to strictly enforce the dlq quota.

This patch fixes both (1) and (2) and updates the unit tests.

[coveralls]

Coverage increased (+0.1%) to 54.548% when pulling 92a655d on dlq-extent into f0355ed on master.

[coveralls]

Coverage increased (+0.1%) to 54.539% when pulling 92a655d on dlq-extent into f0355ed on master.

[coveralls]

Coverage increased (+0.2%) to 54.695% when pulling 9d3de8d on dlq-extent into 8bbdbd7 on master.

[coveralls]

Coverage decreased (-0.3%) to 54.749% when pulling f77aac2 on dlq-extent into 9bf39e1 on master.

[coveralls]

Coverage increased (+0.02%) to 54.634% when pulling 9752887 on dlq-extent into 026daaa on master.

[aravindvs]

lgtm!