util: add New* funcs for ErrKeyNotFound & ErrPoolNotFound types
util: add New* funcs for ErrKeyNotFound & ErrPoolNotFound types

These types have private fields but we need to construct them outside of
the util package. Add New* methods for both.

Signed-off-by: John Mulligan <eda8ad33169deab44f9fe65847f99e368da6c91b@redhat.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi