test: add command to 'Lab failure' timeout message

test: add command to 'Lab failure' timeout message

When a timeout occurs while executing a command a 'Lab failure' message is
written and testing is stopped. The user is left in the dark about the
failure cause.

    ! _pytest.outcomes.Exit: Lab failure: Marking connection bad - no other tests will run !

Add the word 'Timeout' and the executed command to the message.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>