The new tool 'iscsi-md5sum' is used to calculate MD5 value of an iSCSI
target. This help users to verify data at range [LBA, Length).
For example, double-write on a RAID1 of 2 iSCSI targets, a daemon
process runs iscsi-md5sum to check data periodically.
Originally, we have to use several steps to achieve:
1, use iscsiadm to login.(root privilege required)
2, use dd(dd if=/dev/sdX of=/TMPPATH bs=4k count=LENGTH skip=LBA)
to dump data. (root privilege required, additional disk space required)
3, use md5sum to calculate MD5 value
4, remove data.
Instead, a single command iscsi-md5sum without root privilege is enough.
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>