VTL: Fix issue with ipaddress library use under python2.

VTL:  Fix issue with ipaddress library use under python2.

If you pass in a non-unicode 4-byte ipv6 address to ip_address,
ipaddress interprets this as an IPv4Address.

Under python2, ip_address  interprets 'a7::' as a packed ipv4:
 97.55.58.58

You can test with:
---
import ipaddress
try:
    text_type = unicode
except NameError:
    text_type = str

addr = ipaddress.ip_address('a7::')
print(addr)
---

Change-Id: I06c561e0ab7315869cc89d0bb08c05e743a90982
Signed-off-by: Paul Vinciguerra <[email protected]>