The logic for reviewer suggestion only includes groups which have at
least one member which can see the specified change. This automatically
means that groups without members don't see any changes and never show
up in any suggestions. However, some of the tests assumed that group3
(without any explicitly specified members) could still see a created
change. This only worked as the admin user was automatically added. The
new test API for groups doesn't automatically add the admin user. Hence,
we now add another user so that group3 can still see created changes.
Change-Id: If6ad8ebf43e9e1ebbd4965712a5466321094e013
23eacbedad