Simplify return value to "True".

It is fine to return True here because, in the event that the directory
cannot be created, an exception can be raised anyway.

salt/modules/file.py

@@ -4586,7 +4586,7 @@ def mkdir(dir_path,
         # to follow the principal of least surprise method.
         makedirs_perms(directory, user, group, mode)
 
-    return os.path.isdir(directory)
+    return True
 
 
 def makedirs_(path,