tests: allow running Ansible tests locally without -udmw again.

tests/ansible/hosts/default.hosts

@@ -1,8 +1,9 @@
 # vim: syntax=dosini
 
 # When running the tests outside CI, make a single 'target' host which is the
-# local machine.
-target ansible_host=localhost
+# local machine. The ansible_user override is necessary since some tests want a
+# fixed ansible.cfg remote_user setting to test against.
+target ansible_host=localhost ansible_user="{{lookup('env', 'USER')}}"
 
 [test-targets]
 target