Hostname support for WikimediaDefaultSiteTestCase

The test framework now expects a hostname for each site, so
it can verify the site is working before running tests.
That feature fails on WikimediaDefaultSiteTestCase, as it
changes the sites object after the main initialisation code
has been completed.  Add the hostname manually.

Change-Id: I6abb60697dacef698daa03b684e48f8088e52255
Merge "Hostname support for WikimediaDefaultSiteTestCase"