Horizon container restarting due to 'Couldn't find any precompiler in COMPRESS_PRECOMPILERS setting for mimetype text/javascript' error

Issue

• After completing a minor update, Horizon becomes unresponsive

• The Horizon containers on all 3 controllers are in a restarting loop ending with the following error:

  CommandError: An error occurred during rendering /usr/lib/python3.6/site-packages/openstack_dashboard/templates/horizon/_scripts.html: Couldn't find any precompiler in COMPRESS_PRECOMPILERS setting for mimetype '\'text/javascript\''.