Fix docker-swarm for multi-ip machines

Added variable docker_swarm_advertise_addr which can be set to the
advertise address swarm should use.

Mostly introduced for vagrant-based test setups for now, which contain
multiple IP addresses and fail otherwise.

ansible.cfg

@@ -1,4 +1,3 @@
 [defaults]
 
-inventory = ./inventory
+inventory = ./staging
-group = testing

group_vars/testing.yml

@@ -0,0 +1,3 @@
+---
+
+docker_swarm_advertise_addr: eth1

roles/docker-swarm/tasks/main.yml

@@ -3,11 +3,19 @@
 # needs community docker module installed:
 # run $`ansible-galaxy collection install community.docker`
 
-- name: Ensure swarm is initialized
+- name: Ensure swarm is initialized with default advertise address
   community.docker.docker_swarm:
     state: present
-    # advertise_addr: eth1 # necessary for testing setup on vagrant
   become: true
+  when: docker_swarm_advertise_addr is undefined
+
+# ensure setups with multiple ip addresses can be initialized
+- name: Ensure swarm is initialized with specified advertise address
+  community.docker.docker_swarm:
+    state: present
+    advertise_addr: "{{ docker_swarm_advertise_addr }}"
+  become: true
+  when: docker_swarm_advertise_addr is defined
 
 - name: Ensure public network exists
   community.docker.docker_network: