g-s-s uses the wrong IP for the keystone endpoint, leads to juju bootstrap failure

This problem has been observed several times during landscape autopilot CI testing. The observed failure is a failed juju bootstrap with the debug messages:

keystone charm: cs:~openstack-charmers-next/xenial/keystone-281
glance-simplestreams-sync charm: cs:xenial/glance-simplestreams-sync-11

[from console logs (copied to https://pastebin.canonical.com/178802/)]
05:40:32 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:04 DEBUG juju.environs.bootstrap bootstrap.go:571 constraints for image metadata lookup &{{{region1 http://10.96.64.28:5000/v2.0} [xenial win2012hvr2 win2012r2 precise quantal raring utopic vivid win2008r2 win2012hv genericlinux zesty win2016 centos7 saucy trusty wily yakkety win8 win81 win10 win2012 win2016hv win2016nano win7] [amd64 i386 armhf arm64 ppc64el s390x] released}}
05:40:32 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:05 DEBUG juju.environs.simplestreams simplestreams.go:454 skipping index "http://10.96.64.31:8080/v1/AUTH_5720f9bbc9d34ef59f1aa378be68463a/simplestreams/data/streams/v1/index.json" because of missing information: index file has no data for cloud {region1 http://10.96.64.28:5000/v2.0} not found
05:40:32 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:05 DEBUG juju.environs.bootstrap bootstrap.go:579 ignoring image metadata in keystone catalog: index file has no data for cloud {region1 http://10.96.64.28:5000/v2.0} not found
05:40:33 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:06 DEBUG juju.environs.bootstrap bootstrap.go:583 found 0 image metadata in default cloud images
05:40:33 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:06 DEBUG juju.environs.simplestreams simplestreams.go:454 skipping index "http://cloud-images.ubuntu.com/releases/streams/v1/index.sjson" because of missing information: index file has no data for cloud {region1 http://10.96.64.28:5000/v2.0} not found
05:40:33 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:06 DEBUG juju.environs.bootstrap bootstrap.go:579 ignoring image metadata in default ubuntu cloud images: index file has no data for cloud {region1 http://10.96.64.28:5000/v2.0} not found
05:40:33 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:06 DEBUG juju.environs.bootstrap bootstrap.go:587 found 0 image metadata from all image data sources
05:40:33 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:06 INFO juju.provider.common destroy.go:20 destroying model "controller"
05:40:33 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:06 INFO juju.provider.common destroy.go:31 destroying instances
05:40:37 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:10 DEBUG juju.provider.openstack provider.go:1127 terminating instances []
05:40:37 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:10 DEBUG goose <autogenerated>:22 performing API version discovery for "http://10.96.63.239:9696/"
05:40:37 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:10 WARN goose <autogenerated>:38 discovered API versions: [{Version:{major:2 minor:0} Links:[{Href:http://10.96.63.239:9696/v2.0 Rel:self}] Status:CURRENT}]
05:40:37 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:10 INFO juju.provider.common destroy.go:51 destroying storage
05:40:37 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:10 DEBUG juju.provider.openstack cinder.go:81 volume URL: http://10.96.64.32:8776/v2/8a0556c51d51437ba1c1a3ae36e305fb
05:40:40 INFO ui.openstack.test_region_juju_bootstrap.RegionBootstrapTest.test_juju_bootstrap_kvm . 05:40:13 ERROR cmd supercommand.go:458 failed to bootstrap model: no image metadata found

Of note is the line: "index file has no data for cloud {region1 http://10.96.64.28:5000/v2.0} not found".

The simplesteams data it is parsing is:
[from http://10.96.64.31:8080/v1/AUTH_5720f9bbc9d34ef59f1aa378be68463a/simplestreams/data/streams/v1/index.json]
{
 "format": "index:1.0",
 "index": {
  "auto.sync": {
   "cloudname": "glance-simplestreams-sync-openstack",
   "clouds": [
    {
     "endpoint": "http://10.96.64.57:5000/v2.0",
     "region": "region1"
    }
   ],
   "datatype": "image-ids",
   "format": "products:1.0",
   "path": "streams/v1/auto.sync.json",
   "products": [
    "com.ubuntu.cloud:server:14.04:amd64",
    "com.ubuntu.cloud:server:16.04:amd64"
   ],
   "updated": "Thu, 09 Feb 2017 05:09:38 +0000"
  }
 },
 "updated": "Thu, 09 Feb 2017 05:08:26 +0000"
}

There is a mismatch between the endpoint that juju is looking for, "http://10.96.64.28:5000/v2.0" and the one advertised in the index.json, "http://10.96.64.57:5000/v2.0". "10.96.64.28" is the VIP for keystone, while "10.96.64.57" is the private IP of keystone-0. Somehow, glance-simplestreams-sync was given the wrong IP to use for the endpoint and it populated that into the simplestreams data.