Just been trying to install CiviCRM 5.0.1 in Drupal 7.58, and when I try to run the install script, I get a message saying I don't have permission to do so:
"You don't have permission to access this page The installer can only be run by a user with the permission to administer site configuration.
Refer to the online documentation for more information: Installation Guide"
It's a fresh installation of Drupal, and only has the initial admin user - there's nothing unchecked in the Drupal permissions for administrators (but obviously it doesn't have anything related to CiviCRM as the module isn't enabled).