[libmultipath] move coalesce_path() to libmultipath/configure.c

[libmultipath] move coalesce_path() to libmultipath/configure.c

and consequences ...

- coalesce_paths() and all functions used only in this code path are
  folded into configure.c
- move print_*() to libmultipath/print.c, although they are only needed
  for multipath(8) (in their current form)
- declare {map,path}_layout as globals in print.c so we can now remove
  them from the parameter list in all print.c-exported functions

Now we can use coalesce_path() from multipathd.