Description of problem:
When specify invalid ipv6 in --ip-address, ipa-client-install shows traceback

Version-Release number of selected component (if applicable):
4.4.0-11

How reproducible:
always

Steps to Reproduce:
1. ipa-client-install --ip-address 2002:2244:6644:/128

Actual results:
[root@rhel06 ~]# ipa-client-install --ip-address 2002:2244:6644:/128
WARNING: ntpd time&date synchronization service will not be configured as
conflicting service (chronyd) is enabled
Use --force-ntpd option to disable it and force configuration of ntpd

Traceback (most recent call last):
File "/usr/sbin/ipa-client-install", line 3128, in <module>
sys.exit(main())
File "/usr/sbin/ipa-client-install", line 3109, in main
rval = install(options, env, fstore, statestore)
File "/usr/sbin/ipa-client-install", line 2306, in install
if not check_ip_addresses(options):
File "/usr/sbin/ipa-client-install", line 1793, in check_ip_addresses
ipautil.CheckedIPAddress(ip, match_local=True)
File "/usr/lib/python2.7/site-packages/ipapython/ipautil.py", line 138, in init
super(CheckedIPAddress, self).init(addr)
File "/usr/lib/python2.7/site-packages/ipapython/ipautil.py", line 123, in init
self._net = netaddr.IPNetwork(addr, flags=self.netaddr_ip_flags)
File "/usr/lib/python2.7/site-packages/netaddr/ip/init.py", line 926, in init
raise AddrFormatError('invalid IPNetwork %s' % addr)
netaddr.core.AddrFormatError: invalid IPNetwork 2002:2244:6644:/128

Expected results:
error message of invalid IP specified