lib/list_sort: test: unify test messages

This patch unifies 'list_sort_test()' messages a bit and makes sure all of
them start with the "list_sort_test:" prefix to make it obvious for users
where the messages come from.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: Don Mullis <don.mullis@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>