Fix flaky test: avoid ActionMailer static text test over newline
Fix flaky test: avoid ActionMailer static text test over newline

 - waitlist_reminder test is matching text written into the
   view. As you would expect this works 99% of the time. However,
   occasionally, it fails to match in the CI, Travis, and produces
   an error that it can't find the string.
 - Best guess is that it is because of the newline added by the mailer
   system (=0D)
 - Testing a static string in the view adds no value
   - we can see the text in waiting_list_reminder.html.haml
   - we already test the subject which is also unique
 - Keep the dynamic text test but with shorter static text
 - Summary: I do not know why this error occurs. Just testing long
   static text adds nothing except another flaky test. We should
   want to avoid it.

codebar/planner,laszpio/planner,codebar/planner,despo/planner,codebar/planner,despo/planner,codebar/planner,laszpio/planner,despo/planner,laszpio/planner,despo/planner,laszpio/planner