Replicator: use cmd_vg list for _process_one_vg()

Replicator: use cmd_vg list for _process_one_vg()

Patch modifes behavior of _process_one_vg().

In the first pass vg_read() collectis for replicator sorted list of
additional VGs during lock_vol().
If any other VG is needed by the replicator and it is not yet opened
then next iteration loop is taken with all collected VGs.

Flag vg->cmd_missing_vgs detects missing VGs.