Hibernate: fix the race condition of remove S4 sign key

This patch fix the race condition of remove S4 sign key. It moved the
code of reload sign key  to software_resume() in hibernate.c after we
confirmed the snapshot image doesn't in swap partition. We ignore the
errors, -ENOENT, -ENODEV and -NENXIO to ignore the checking result before
swap partition available. It avoid the S4 sign key removed before we
load it after S4 resume success.

Signed-off-by: Lee, Chun-Yi <jlee@suse.com>