ansible-doc-test: Set ANSIBLE_LIBRARY using module_dir internally

ANSIBLE_LIBRARY needs to be set properly for new Ansible version 4.0.0
to make sure that it is able to find the module that is checked.

For every file that needs to be checked, there is a separate ansible-doc
call. ANSIBLE_LIBRARY is set using os.path.dirname on the module_path.

utils/ansible-doc-test

@@ -29,12 +29,16 @@ import subprocess
 
 def run_ansible_doc(role, module, verbose=False):
     playbook_dir, module_path = get_playbook_dir(role, module)
+    module_dir = os.path.dirname(module_path)
 
-    command = ["ansible-doc",
+    command = ["env",
+               "ANSIBLE_LIBRARY=%s" % module_dir,
+               "ansible-doc",
                "--playbook-dir=%s" % playbook_dir,
                "--type=module",
                "-vvv",
                module]
+
     process = subprocess.run(command,
                              stdout=subprocess.PIPE,
                              stderr=subprocess.PIPE)