iscsi-target: TargetAddress in SendTargets should bracket ipv6 addresses

"The domainname can be specified as either a DNS host name, a
dotted-decimal IPv4 address, or a bracketed IPv6 address as specified
in [RFC2732]."

See https://bugzilla.redhat.com/show_bug.cgi?id=1206868



Reported-by: Kyle Brantley <kyle@averageurl.com>
Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>