v3: ensure that polling interval is an int

[#174144484](https://www.pivotaltracker.com/story/show/174144484)

Author: Derik Evangelista

app/jobs/reoccurring_job.rb

@@ -34,6 +34,7 @@ def polling_interval_seconds
       end
 
       def polling_interval_seconds=(interval)
+        interval = interval.to_i if interval.is_a? String
         @polling_interval = if interval < default_polling_interval_seconds
                               default_polling_interval_seconds
                             elsif interval > 24.hours

spec/unit/jobs/reoccurring_job_spec.rb

@@ -100,7 +100,7 @@ def perform
 
       context 'updates the polling interval if config changes' do
         it 'when changed from the job only' do
-          job = FakeJob.new(retry_after: [20, 30])
+          job = FakeJob.new(retry_after: ['20', '30'])
           TestConfig.config[:broker_client_default_async_poll_interval_seconds] = 10
 
           enqueued_time = Time.now