spec: refactor more assignment selenium specs for draft state

refs #CNVS-15563

Change-Id: I3bd76074387ea2a0a095441547bf56f39322948b
Reviewed-on: https://gerrit.instructure.com/43477
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>