Allow course home behavior configuration to override unified course tab

[kaizoku]

This PR amends a previous change (fe95b2b), which allows for configuring where the root URL of a course redirects to.

This older commit ignores the added configuration value if the unified course tab is set, but this removes the option to set the course root redirection when the unified course tab is enabled.

Here we move the check for the COURSE_HOME_BEHAVIOUR option from the SiteConfiguration to before checking the unified course tab to allow us to still configure this when the unified course tab is enabled.

JIRA tickets: Implements BB-3399

Discussions: Discussed on JIRA

Dependencies: None

Merge deadline: ASAP

Testing instructions:

1. Set course_experience.unified_course_tab flag to true in your devstack WaffleFlag settings
2. In your devstack site configuration set the following value: "COURSE_HOME_BEHAVIOUR":"courseware",
3. Visit a course root such as http://localhost:18000/courses/course-v1:edX+DemoX+Demo_Course/
4. Verify that this redirects directly to the courseware

Reviewers

• (@AdditionalPylons)

[AdditionalPylons]

• I applied the change and verified that visiting a course root redirects directly to courseware