Remove unneeded required_one_of for openstack

We're being too strict - there is a third possibility, which is that a
user will have defined the OS_* environment variables and expect them to
pass through.

lib/ansible/module_utils/openstack.py

@@ -93,11 +93,7 @@ def openstack_full_argument_spec(**kwargs):
 
 
 def openstack_module_kwargs(**kwargs):
-    ret = dict(
-        required_one_of=[
-            ['cloud', 'auth'],
-        ],
-    )
+    ret = {}
     for key in ('mutually_exclusive', 'required_together', 'required_one_of'):
         if key in kwargs:
             if key in ret:

lib/ansible/utils/module_docs_fragments/openstack.py

@@ -23,7 +23,9 @@ class ModuleDocFragment(object):
 options:
   cloud:
     description:
-      - Named cloud to operate against. Provides default values for I(auth) and I(auth_plugin)
+      - Named cloud to operate against. Provides default values for I(auth) and
+        I(auth_type). This parameter is not needed if I(auth) is provided or if
+        OpenStack OS_* environment variables are present.
     required: false
   auth:
     description:
@@ -32,7 +34,8 @@ options:
         I(auth_url), I(username), I(password), I(project_name) and any
         information about domains if the cloud supports them. For other plugins,
         this param will need to contain whatever parameters that auth plugin
-        requires. This parameter is not needed if a named cloud is provided.
+        requires. This parameter is not needed if a named cloud is provided or
+        OpenStack OS_* environment variables are present.
     required: false
   auth_type:
     description:

v2/ansible/module_utils/openstack.py

@@ -93,11 +93,7 @@ def openstack_full_argument_spec(**kwargs):
 
 
 def openstack_module_kwargs(**kwargs):
-    ret = dict(
-        required_one_of=[
-            ['cloud', 'auth'],
-        ],
-    )
+    ret = {}
     for key in ('mutually_exclusive', 'required_together', 'required_one_of'):
         if key in kwargs:
             if key in ret: