osduld: Add osdname & systemid sysfs at scsi_osd class

This patch adds the support for following two read-only sysfs attributes
to scsi_osd class members : osdname & systemid

These attributes will show up as below in sysfs class hierarchy:
/sys/class/scsi_osd/osdX/osdname
/sys/class/scsi_osd/osdX/systemid

The osdname & systemid are OSD device attributes which uniquely
identify a device on the network, while it's IP and certainly
it's /dev/osdX device path might change.
Userspace utilities (e.g. mkfs.exofs) can parse these attributes to
identify the correct OSD in safer and faster way.

(Today osd apps open each device in the system and send a
 attributes query for these, in order to access the user
 requested device)

Signed-off-by: Sachin Bhamare <sbhamare@panasas.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>