[multipathd] DM configuration ground work

[multipathd] DM configuration ground work

- introduce update_mpp_paths() to refresh mpp->paths out of mpp->pg
- fix 2 segfault in uev_{add,del}_path logging in error paths
- split add_map_without_path() out of uev_add_map()
- adopt_paths() to take a pathvec as 1st param instead of a full "vecs"
- select round robin weights in setup_multipath()
- uev_add_map to return if map is already registered instead of the purge
  plus re-register cycle