remove listen directive bound to only ipv4
remove listen directive bound to only ipv4

Using devstack on a  RHEL based system results in
"Listen 0.0.0.0:80" being added to the
/etc/httpd/conf/httpd.conf.
This configures Apache to only listen to port 80 on an IPv4 interface.
This makes it not possible to access Horizon via IPv6 without
re-configuring and restarting httpd.

Removing this sed leaves the default "Listen 80" from the rpm package,
 which binds to all interfaces and will allow connection to Horizon
via IPv6.

Change-Id: I9fe8cbebff0ca6a30ceeaae0f7e035c9bb828d44

richliu/devstack,openstack-dev/devstack,richliu/devstack,dtroyer/devstack,group-policy/devstack,noironetworks/devstack,openstack-dev/devstack,nawawi/openstack,bswartz/devstack,bswartz/devstack,noironetworks/devstack,nawawi/openstack,dtroyer/devstack,group-policy/devstack