xcp-sm: Update rules and script to work on Ubuntu

Ubuntu's udev no longer recognises the deprecated 'BUS' tag,
and it installs scsi_id in /lib/udev rather than in /usr/sbin.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #312 from euanh/ubuntu-sm

xcp-sm: Update rules and script to work on Ubuntu