tests: define MITOGEN_INVENTORY_FILE even if -i unspecified.

To fix running tests locally.

tests/ansible/run_ansible_playbook.py

@@ -46,6 +46,10 @@ if '-i' in sys.argv:
     extra['MITOGEN_INVENTORY_FILE'] = (
         os.path.abspath(sys.argv[1 + sys.argv.index('-i')])
     )
+else:
+    extra['MITOGEN_INVENTORY_FILE'] = (
+        os.path.join(GIT_BASEDIR, 'tests/ansible/hosts')
+    )
 
 args = ['ansible-playbook']
 args += ['-e', json.dumps(extra)]