Use is_valid_ipv4 from oslo.utils

In module netaddr valid_ipv4 raise exception AddrFormatError
if address is specified as empty string. Method is_valid_ipv4
catches the exception and returns boolean value. So we'd better
use it from oslo.utils.

Change-Id: I39d074f451b0e3f7b7203acf69ec4dd791e83114
2 files changed