lower the priority of Course#recache_grade_distribution
lower the priority of Course#recache_grade_distribution

but not to ultra-low priority

Change-Id: I5771c2c2ca5e0675fdc8e1ab03bf5276a419541d
Reviewed-on: https://gerrit.instructure.com/164145
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Tested-by: Jenkins
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

instructure/analytics,instructure/analytics,instructure/analytics