Split on newlines when checking for prompt matches (#20945)

* Check for the prompt as a substring of the output

sudo sometimes spits out warnings to stdout before getting to the
password prompt.  Account for that when trying to match a password
prompt.

Fixes #20858

lib/ansible/plugins/connection/__init__.py

@@ -254,7 +254,7 @@ class ConnectionBase(with_metaclass(ABCMeta, object)):
             return False
         elif isinstance(self._play_context.prompt, string_types):
             b_prompt = to_bytes(self._play_context.prompt)
-            return b_output.startswith(b_prompt)
+            return b_prompt in b_output
         else:
             return self._play_context.prompt(b_output)