fix hide_from_students being ignored on new pages

test plan:
 - on a course with draft state disabled
 * create a new page through the api (using both POST and PUT)
   - with wiki_page[hide_from_students] set to 'false'
 - the page should be created with hide_from_students set to 'false'

fixes CNVS-10096

Change-Id: Idaa96c6dc358d929eed69566df363ed614b6f1e8
Reviewed-on: https://gerrit.instructure.com/28240
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>