Replace the base_url in the OAuth2 redirect uri checks

Summary:
This fixes oauth authorization requests when deployed in a subdirectory.
It assumes that the redirect_uri in the DB is relative to the base url.

Refs T331

Test Plan:
- Configure your deployments in a subdir and check you can log in to the UI.
- Check again with index.php configured in your urls.

Reviewers: shadowhand, eyedol

Reviewed By: shadowhand, eyedol

Maniphest Tasks: T331

Differential Revision: https://phabricator.ushahidi.com/D162