(maint) Update acceptance tests that reference nightlies
(maint) Update acceptance tests that reference nightlies

This commit changes the name of the nightlies server to the actual hostname so
that when we remove the 'nightlies' cname (to use for *new* nightlies), tests
won't break. THIS SHOULD NOT BE PERMANENT (see RE-10231).

puppetlabs/marionette-collective,puppetlabs/marionette-collective,puppetlabs/marionette-collective,puppetlabs/marionette-collective,puppetlabs/marionette-collective,puppetlabs/marionette-collective