test: less fragile integration suite [ci skip]

See coop-cloud/organising#584
See coop-cloud/organising#595

tests/integration/app_services.bats

@@ -19,10 +19,7 @@ setup(){
 }
 
 teardown(){
-  # https://github.com/bats-core/bats-core/issues/383#issuecomment-738628888
-  if [[ -z "${BATS_TEST_COMPLETED}" ]]; then
-    _undeploy_app
-  fi
+  _undeploy_app
 }
 
 @test "validate app argument" {
@@ -51,6 +48,4 @@ teardown(){
   sanitisedDomainName="${TEST_APP_DOMAIN//./_}"
   assert_output --partial "$sanitisedDomainName_app"
   assert_output --partial "nginx"
-
-  _undeploy_app
 }