make inventory warnings a bit smarter (#46284)

less annoying for common cases
 add comment for 'tricky' conditional

lib/ansible/cli/__init__.py

@@ -807,7 +807,7 @@ class CLI(with_metaclass(ABCMeta, object)):
         no_hosts = False
         if len(inventory.list_hosts()) == 0:
             # Empty inventory
-            if C.LOCALHOST_WARNING:
+            if C.LOCALHOST_WARNING and pattern not in C.LOCALHOST:
                 display.warning("provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'")
             no_hosts = True