tests: use baseurl instead of advertisedbaseurl
The distinction matters for e.g. hosts behind load balancers. But for
the test environment, it doesn't matter.
For whatever reason, advertisedbaseurl is resolving to
http://1.0.0.127.in-addr.arpa:$HGPORT on my MBP. This hostname fails
to resolve, causing the test to fail. No clue what's up with that
behavior.
Differential Revision: https://phab.mercurial-scm.org/D4973