Unit Tests, Groups: update the Group factory to handle `false` return values from `groups_create_group`.

It currently assumes that the group is always succesfully created, and this isn't true if `creator_id` is set to `0` (or if there is no logged in user).

See #5983

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9117 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Unit Tests, Groups: test group creation for authenticated vs anonymous user.

These will fail until I get a subsequent commit in; I wanted these in first so we can easily see if the fix works as expected.

See #5983

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9118 cdf35c40-ae34-48e0-9cc9-0c9da1808c22