Fix non-matching defaults. (#494) (#496)

(cherry picked from commit 1ac3a99e7c)

Co-authored-by: Felix Fontein <felix@fontein.de>

plugins/modules/docker_network.py

@@ -30,6 +30,7 @@ options:
         M(community.docker.docker_container) module to ensure your containers are correctly connected to this network.
     type: list
     elements: str
+    default: []
     aliases:
       - containers
 
@@ -43,6 +44,7 @@ options:
     description:
       - Dictionary of network settings. Consult docker docs for valid options and values.
     type: dict
+    default: {}
 
   force:
     description:
@@ -130,6 +132,7 @@ options:
     description:
       - Dictionary of labels.
     type: dict
+    default: {}
 
   scope:
     description:

plugins/modules/docker_plugin.py

@@ -47,6 +47,7 @@ options:
     description:
       - Dictionary of plugin settings.
     type: dict
+    default: {}
 
   force_remove:
     description:

plugins/modules/docker_volume.py

@@ -34,6 +34,7 @@ options:
       - "Dictionary of volume settings. Consult docker docs for valid options and values:
         U(https://docs.docker.com/engine/reference/commandline/volume_create/#driver-specific-options)."
     type: dict
+    default: {}
 
   labels:
     description: