Line continuations and not simple "\n" for the json output, this got
inherited to the plain text output, but this is not necessary.
This also caused problems in fstests btrfs/006 where the extra newline
does not match the golden output and the test fails, when printing
device stats that now use the output formatter.
Change the plain text formatting to always expect that a fmt_print or a
manual line print (like is for the device stats) will append the newline
and remove it from the end of formatting.
Link: https://lore.kernel.org/linux-btrfs/CAL3q7H4b7QhL02aSOpN0-k_9P2EAbj1t+NkA6VwidKEg4S996w@mail.gmail.com
Reported-by: Filipe Manana <fdmanana@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>