v3(services): don't cache the max polling duration

[#173834127](https://www.pivotaltracker.com/story/show/173834127)

Author: Derik Evangelista

app/jobs/reoccurring_job.rb

@@ -22,7 +22,11 @@ def maximum_duration_seconds
       end
 
       def maximum_duration_seconds=(duration)
-        @maximum_duration = duration if duration < default_maximum_duration_seconds
+        @maximum_duration = if duration.present? && duration < default_maximum_duration_seconds
+                              duration
+                            else
+                              default_maximum_duration_seconds
+                            end
       end
 
       def polling_interval_seconds

app/jobs/v3/service_instance_async_job.rb

@@ -25,10 +25,10 @@ def perform
         raise_if_cannot_proceed!
 
         client = VCAP::Services::ServiceClientProvider.provide({ instance: service_instance })
+        compute_maximum_duration
 
         begin
           if @first_time
-            compute_maximum_duration
             execute_request(client)
             compatibility_checks
             @first_time = false
@@ -139,7 +139,7 @@ def fetch_last_operation(client)
 
       def compute_maximum_duration
         max_poll_duration_on_plan = service_instance.service_plan.try(:maximum_polling_duration)
-        self.maximum_duration_seconds = max_poll_duration_on_plan if max_poll_duration_on_plan
+        self.maximum_duration_seconds = max_poll_duration_on_plan
       end
 
       def service_instance

spec/unit/jobs/v3/service_instance_async_job_spec.rb

@@ -238,6 +238,27 @@ def send_broker_request(_) end
             job.perform
           end
 
+          context 'the maximum duration' do
+            it 'recomputes the value' do
+              job.maximum_duration_seconds = 90009
+              TestConfig.override({ broker_client_max_async_poll_duration_minutes: 8088 })
+              job.perform
+              expect(job.maximum_duration_seconds).to eq(8088.minutes)
+            end
+
+            context 'when the plan value changes between calls' do
+              before do
+                job.maximum_duration_seconds = 90009
+                service_plan.update(maximum_polling_duration: 5000)
+                job.perform
+              end
+
+              it 'sets to the new plan value' do
+                expect(job.maximum_duration_seconds).to eq(5000)
+              end
+            end
+          end
+
           it 'does not send any operation request to the broker' do
             job.perform
             expect(job).to have_received(:send_broker_request).once