This splits commands of storage pool group into virsh-pool.c,
The helpers not for common use are moved too. Standard copyright
is added for the new file.

* tools/virsh.c:
  Remove commands for storage storage pool and a few helpers.
  (vshCommandOptVol, vshCommandOptVolBy).

* tools/virsh-pool.c:
  New file, filled with commands of storage pool group and its
  helpers.

* po/POTFILES.in:
  Add virsh-pool.c

* cfg.mk:
  Skip to check config.h including for virsh-pool.c