test: less fragile integration suite [ci skip]

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

tests/integration/server_add.bats

@@ -3,25 +3,19 @@
 setup_file(){
   load "$PWD/tests/integration/helpers/common"
   _common_setup
-
-  run docker swarm leave --force
 }
 
 setup(){
   load "$PWD/tests/integration/helpers/common"
   _common_setup
-
-  run docker swarm init
-  assert_success
 }
 
 teardown(){
-  run docker swarm leave --force
-  assert_success
-
   _rm_server
+  _ensure_swarm
 }
 
+# bats test_tags=slow,dns
 @test "add new server" {
   run $ABRA server add "$TEST_SERVER"
   assert_success
@@ -57,6 +51,7 @@ teardown(){
   assert_output --partial 'swarm mode not enabled on local server'
 }
 
+# bats test_tags=slow
 @test "cleanup when cannot add server" {
   run $ABRA server add example.com
   assert_failure