Allow IP-based subject alt names
Allow IP-based subject alt names

... even when no other subject alt names provided

Previously, a non-voting job in barbican's gate would fail with something like

  X509 V3 routines:X509V3_parse_list:invalid null name:v3_utl.c:319:
  X509 V3 routines:DO_EXT_NCONF:invalid extension string:v3_conf.c:140:name=subjectAltName,section=DNS:pykmip-server,,IP:198.72.124.103
  X509 V3 routines:X509V3_EXT_nconf:error in extension:v3_conf.c:95:name=subjectAltName, value=DNS:pykmip-server,,IP:198.72.124.103

because we'd have an invalid empty string.

Change-Id: I5459b8976539924cd6cc6c1e681b6753a76b804c

openstack-dev/devstack,nawawi/openstack,openstack-dev/devstack,nawawi/openstack