IPv6 support missing

[Obihoernchen]

The xcat-inventory/xcclient/inventory/vutil.py:isIPaddr(varin) function needs to add support for IPv6 addresses.

Currently xcat-inventory does not allow to import a config with IPv6 addresses.

Example:

Error: failed to validate attribute [basic_attr.mask] of object "2001_123_a123_1456-64", criteria: "value='/64': vutil.isIPaddr(value)"
Error: failed to validate attribute [basic_attr.net] of object "2001_123_a123_1456-64", criteria: "value='2001:123:a123:1456::/64': vutil.isIPaddr(value)"