ansible: add "groups" key to get_variables()

This key was returned by ansible python API in testinfra 2.X and users
rely on it.

Closes #443

test/test_modules.py

@@ -338,6 +338,11 @@ def test_ansible_module(host):
     assert variables["mygroupvar"] == "qux"
     assert variables["inventory_hostname"] == "debian_stretch"
     assert variables["group_names"] == ["testgroup"]
+    assert variables["groups"] == {
+        "all": ["debian_stretch"],
+        "testgroup": ["debian_stretch"],
+        "ungrouped": [],
+    }
 
     with pytest.raises(host.ansible.AnsibleException) as excinfo:
         host.ansible("command", "zzz")

testinfra/utils/ansible_runner.py

@@ -142,16 +142,21 @@ def ansible_config(self):
 
     def get_variables(self, host):
         inventory = self.inventory
+        # inventory_hostname, group_names and groups are for backward
+        # compatibility with testinfra 2.X
         hostvars = inventory['_meta'].get(
             'hostvars', {}).get(host, {})
         hostvars.setdefault('inventory_hostname', host)
-        groups = []
+        group_names = []
+        groups = {}
         for group in sorted(inventory):
-            if group in ('_meta', 'all'):
+            if group == "_meta":
                 continue
-            if host in inventory[group].get('hosts', []):
-                groups.append(group)
-        hostvars.setdefault('group_names', groups)
+            groups[group] = list(itergroup(inventory, group))
+            if group != "all" and host in inventory[group].get('hosts', []):
+                group_names.append(group)
+        hostvars.setdefault('group_names', group_names)
+        hostvars.setdefault('groups', groups)
         return hostvars
 
     def get_host(self, host, **kwargs):