According bug exception trace this problem cause by host name validate .
The origin code use netaddr.IPAddress to validate host name, it just fit ip address,
so the ip/netmask style do not match this rule.To solve this problem,
I changed this method to netaddr.IPNetwork, which support ip and
ip/netmask. Also provide a test case to validate the method.
Change-Id: I8dad9d1496d09372698821b832d1baa4f0c35a0d
Closes-Bug: #1673874