lvmanip: uninitialized members in struct pv_list (#10)

Scenario: Given an existed LV `lvol0`, I want to create another LV
on the PVs used by `lvol0`.

I use `build_parallel_areas_from_lv()` to obtain the `pv_list` of each segments.
However, the returned `pv_list` is not properly initialized, which causes
segfault in subsequent operations.

(cherry picked from commit 859feb8)
(cherry picked from commit 219ba4f)

Conflicts:
	WHATS_NEW

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.184 - 
 =====================================
+ Fix missing proper initialization of pv_list struct when adding pv.
 
 Version 2.02.183 - 07th December 2018
 =====================================

lib/metadata/lv_manip.c

@@ -5860,7 +5860,7 @@ static int _add_pvs(struct cmd_context *cmd, struct pv_segment *peg,
  if (find_pv_in_pv_list(&spvs->pvs, peg->pv))
  return 1;
 
- if (!(pvl = dm_pool_alloc(cmd->mem, sizeof(*pvl)))) {
+ if (!(pvl = dm_pool_zalloc(cmd->mem, sizeof(*pvl)))) {
  log_error("pv_list allocation failed");
  return 0;
  }