Updated scsi path<->hctl utils for PSCSI TYPE_DISK/TYPE_ROM on modern kernels

* Functions rtslib.utils.convert_scsi_path_to_hctl() and
  rtslib.utils.convert_scsi_hctl_to_path() were using
     '/sys/class/scsi_device/$SCSI_HCTL/device/block/$SCSI_DEVICE/'
  which is now absent from modern kernels. Now using
     '/sys/block/$SCSI_DEVICE/device/scsi_device/$SCSI_HCTL'
  which is present in both 2.6x and all 3.x kernels.
src: orthographic fixes

The correct form is "instantiation".
rtslib: make write_protect=0 create read-only mapped LUNs

The write_protect parameter was incorrectly parsed so that whenever it
was specified, even with the value 0, it set the mapped LUN read-only.

	cd /iscsi/iqn.0000-00.a.b/tpgt1/acls/iqn.0000-00.de.suse:foo
	create tpg_lun=0 mapped_lun=0 write_protect=0