Split announcements selenium spec in two

Fixes CNVS-16486

Test Plan:
Ensure tests still pass

Change-Id: Ic794fd02d631c10f6f155f296de41eb00d0fe6dd
Reviewed-on: https://gerrit.instructure.com/43327
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Mark Severson <markse@instructure.com>
Product-Review: Matthew Wheeler <mwheeler@instructure.com>
QA-Review: Matthew Wheeler <mwheeler@instructure.com>