Add missing default case

Silence a warning about a missing case in handle_expected_reply in mxsh.
We're not handling the MxShTaskNone case. Handle it and any other
non-handled task with an empty default case.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Only handle tasks if expected reply was ok

Mxsh will always handle pending tasks no matter what reply it has
received. It will check if it's not an ok reply and print the message it
contains.

Jump past the switch statement where the current task is carried out.
This removes the need to check if it was an ok reply, such as in the
case of MxShTaskStarttls where we don't want to proceed with the
handshake if the command was unsuccessful.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>