The fix for leading junk in sudo output: fee6e29 causes problems with
ssh + sudo. On the initial connection using ControlPersist, the output
that we scan for the prompt contains both the command we're sending to
configure the prompt and the prompt itself. The code in fee6e29 ends up
sending the password when it sees the line configuring the prompt which
is too early.
Switch to a version that splits on lines and then checks whether the
first or last line starts with the prompt to decide if it's time to send
the password.
Fixes#23054
References #20858
6f77498700