Support string interval coming from report preview

I hit this when running the UI tests without a simulate_queue_worker running.
I believe this is a bug that can happen where this code path provides an interval
of type string.

With no workers running, such as rails server with no simulate queue worker:
Go to: Overview->Reports->Reports accordion->Configuration->New Report

Give it a name, title, "base the report on" such as availability zone,
add a field such as Ems Ref to the selected fields.  Then, click "preview" tab.
Click "generate report preview" button... Before this change, it blows up with:

[TypeError] no implicit conversion of Integer into String

Note, this is a similar change as #9444

Author: jrafanie

app/controllers/application_controller/wait_for_task.rb

@@ -11,7 +11,7 @@ def wait_for_task
     @edit = session[:edit]  # If in edit, need to preserve @edit object
     raise Forbidden, _('Invalid input for "wait_for_task".') unless params[:task_id]
 
-    async_interval = params[:async_interval] || 1000 # Default interval to 1 second
+    async_interval = params.fetch(:async_interval, 1000).to_i # Default interval to 1 second
 
     task = MiqTask.find(params[:task_id].to_i)
     if task.state != "Finished" # Task not done --> retry