caddy-frontend: Follow SlapOS guidelines about instance processing

Drop hacks applied in the test, so that it will uncover all missing promises
and corner cases.

software/caddy-frontend/test/test.py

@@ -82,9 +82,6 @@ else:
     os.path.abspath(
         os.path.join(os.path.dirname(__file__), '..', 'software.cfg')))
 
-  # XXX Keep using slapos node instance --all, because of missing promises
-  SlapOSInstanceTestCase.slap._force_slapos_node_instance_all = True
-
 # ports chosen to not collide with test systems
 HTTP_PORT = '11080'
 HTTPS_PORT = '11443'