Make tests more resilient to slow emit stats

Without the `eval` instructions, the stats were emitted "too slowly",
and some tests expect metrics to be available sooner. The update to the
Makefile ensures that stats are emitted "quickly". Those instructions
are borrowed from the CI scripts in bin/

The expectations in the test prevent a panic when the stats are not
emitted fast enough.

Makefile

@@ -44,3 +44,5 @@ docker.rabbitmq:
 	docker exec -ti rabbithole_rabbitmq /bin/bash -c "rabbitmqctl set_permissions -p rabbit/hole guest \".*\" \".*\" \".*\""
 	docker exec -ti rabbithole_rabbitmq /bin/bash -c "rabbitmqctl set_permissions -p rabbit/hole policymaker \".*\" \".*\" \".*\""
 	docker exec -ti rabbithole_rabbitmq /bin/bash -c "rabbitmq-plugins enable rabbitmq_federation rabbitmq_federation_management rabbitmq_shovel rabbitmq_shovel_management"
+	docker exec -ti rabbithole_rabbitmq rabbitmqctl eval 'supervisor2:terminate_child(rabbit_mgmt_sup_sup, rabbit_mgmt_sup), application:set_env(rabbitmq_management,       sample_retention_policies, [{global, [{605, 1}]}, {basic, [{605, 1}]}, {detailed, [{10, 1}]}]), rabbit_mgmt_sup_sup:start_child().'
+	docker exec -ti rabbithole_rabbitmq rabbitmqctl eval 'supervisor2:terminate_child(rabbit_mgmt_agent_sup_sup, rabbit_mgmt_agent_sup), application:set_env(rabbitmq_management_agent, sample_retention_policies, [{global, [{605, 1}]}, {basic, [{605, 1}]}, {detailed, [{10, 1}]}]), rabbit_mgmt_agent_sup_sup:start_child().'

rabbithole_test.go

@@ -816,6 +816,8 @@ var _ = Describe("RabbitMQ HTTP API client", func() {
 			Ω(q.Name).ShouldNot(Equal(""))
 			Ω(q.Node).ShouldNot(BeNil())
 			Ω(q.Durable).ShouldNot(BeNil())
+			Ω(q.MessagesDetails).ShouldNot(BeNil(),
+				"messages details are nil, this happens when stats are not emitted fast enough. Check docker.rabbitmq Make target for a hint to resolve this")
 			Ω(q.MessagesDetails.Samples[0]).ShouldNot(BeNil())
 		})
 	})
@@ -861,6 +863,8 @@ var _ = Describe("RabbitMQ HTTP API client", func() {
 			Ω(q.Node).ShouldNot(BeNil())
 			Ω(q.Vhost).Should(Equal(vh))
 			Ω(q.Durable).ShouldNot(BeNil())
+			Ω(q.MessagesDetails).ShouldNot(BeNil(),
+				"messages details are nil, this happens when stats are not emitted fast enough. Check docker.rabbitmq Make target for a hint to resolve this")
 			Ω(q.MessagesDetails.Samples[0]).ShouldNot(BeNil())
 
 			rmqc.DeleteQueue(vh, qn)