Improve tests for get_blogs_of_user()

[jeremyfelt]

Our current multisite test for get_blogs_of_user() creates a user and 10 new sites, removes the user from the primary site on the network, and then tests to see if the user is still a member of those 10 sites. It also duplicates some of the efforts of our single site test, which handles the multisite case for a deleted user.

We can expand coverage a bit in get_blogs_of_user() and gain some speed / reduce duplicity.

[jeremyfelt]

In 29996.diff, we:

• Create 8 new sites rather than 10. This is pretty arbitrary, as we don't need all of them. It is nice to know that things work though.
• Remove the user from multiple sites rather than only the first. This reduces the number of overall assertions that we make and helps to ensure that get_blogs_of_user() continues to provide accurate data.
• Remove duplicate assertions for logged out users and deleted users, these are available in the single site test for get_blogs_of_user(). The one piece missing from the single site version is moved over.

And... accidentally leave bad docs for the test method. :) Do we have doc standards for tests yet?

[jeremyfelt]

29996.2.diff adds more assertions to test the second parameter of get_blogs_of_user() by marking sites as spam, archived, and deleted.

[jeremyfelt]

In 29937:

Improve and reduce tests for get_blogs_of_user()

• Create half as many factory sites. See #30017
• Test the removal of a user from multiple sites.
• Expand tests to include second parameter for flagged sites.
• Remove duplicate test for deleted user.

Fixes #29996