event stream is requiring a cassandra database to be configured.

fixes: CNVS-13056

Test Case:

  Make sure cassandra is not configured in cassandra.yml.
  Event stream should not complain about it not being configured.

Change-Id: If6a6583be355672f9a24769caf5e2da663a336a8
Reviewed-on: https://gerrit.instructure.com/34926
Reviewed-by: Brian Palmer <brianp@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Nick Cloward <ncloward@instructure.com>