[multipath] get_refwwid() tweaking
[multipath] get_refwwid() tweaking

- don't recode strdup() everywhere
- get_user_friendly_wwid() does allocate, not need to strdup() again.
  This was a leak proper


gebi/multipath-tools,unakatsuo/multipath-tools,vijaychauhan/multipath-tools,unakatsuo/multipath-tools,grzn/multipath-tools-explained,vijaychauhan/multipath-tools,unakatsuo/multipath-tools,grzn/multipath-tools-explained