change text for "Choose Home Page" in new course wizard

fixes CNVS-12747

test plan:
 - create a new course in a draft-state-enabled account
 - click "Choose a Course Home Page" in the bottom panel
 - the description on the right should match the button in the
   right sidebar ("Choose Home Page" instead of "Set Course Layout")

Change-Id: I0178fe369c89e58923e25fc4249b480813e3ec3c
Reviewed-on: https://gerrit.instructure.com/36560
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>