nonha: fix memcached servers string in nova.conf for ipv6
nonha: fix memcached servers string in nova.conf for ipv6

Full context is described here:
https://review.openstack.org/#/c/270110/

The patch that was supposed to fix [1] was not fixing non-ha scenario.
[1] https://launchpad.net/bugs/1536103

This patch aims to fix it.

Change-Id: Iaf4608de1894ce03f35925939e83230abb9f5207
Closes-Bug: #1560063

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,bcrochet/tripleo-heat-templates,bcrochet/tripleo-heat-templates,trozet/opnfv-tht,bcrochet/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,trozet/opnfv-tht,trozet/opnfv-tht