Set several site tests to be logged in

Several site tests depend on site.user() returning a valid
username.  These have been moved into a specific class, with
'user = True' set.

Improve 'user = True' so that it logs in before each test if
the site has become logged out during a different test.

Change-Id: I2e218471d99bc7ad23f42570157e9fd80432716e