Multisite suggestions tests should not use 'admin' as current_user username

[boonebgorges]

There's a quirk in the core multisite unit test suite such that when you run create_user() with the username 'admin', that user becomes a super admin on the network; as such, the user has the 'bp_moderate' cap, and is able to get suggestions for all members. This breaks some of the suggestions unit tests, which assume that the logged-in user will not have access to the members of certain groups.

Solution appears to be to use a different username than 'admin' for the user that the tests are run as.

[boonebgorges]

In 8562:

Don't use 'admin' as the username of the user when running suggestions tests

On multisite, this user is granted super admin privileges, which breaks some of
the tests.

Fixes #5744

[DJPaul]

Nice, thanks.