logger: add a newline to the end of print format if it is missing

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
checkpatch: show warning if sd_printf format string contains a newline

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
remove newline from sd_printf format string

This simplifies codes a bit.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
checkpatch: add check for strerror(errno)

For simplicity, let's use %m instead.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
sheep: use %m instead of strerror(errno)

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>