hibernate-util: log that we actually read /sys/power/resume* rather than cmdline

hibernate-util: log that we actually read /sys/power/resume* rather than cmdline

/sys/power/resume is always populated by the initrd, while
/sys/power/resume_offset might have been populated by
the kernel itself. Therefore, if the user is using an initrd
that doesn't include resume hook, the hibernation would fail,
which is expected. However, it was hard to track down the real
problem, since the previous log message suggested that resume=
is not set through kernel cmdline.