Fixes WEBSSO_KEYSTONE_URL Value

Change I60162b54bc06e158534d29311d4474b34750c64d
removed the `/v3` prefix from the WEBSSO_KEYSTONE_URL
variable. However, keystone endpoints do in fact
have the `/v3` prefix, and Horizon expects the
WEBSSO_KEYSTONE_URL variable to already contain
the prefix.

This patch adds the prefix again so that SSO
works with Horizon again.

Closes-Bug: #2028921
Change-Id: I5799f7a6fa4f52c2904b14fc02ed18443f4194bd
Signed-off-by: Juan Pablo Suazo <jsuazo@whitestack.com>

ansible/roles/horizon/templates/local_settings.j2

@@ -224,7 +224,7 @@ WEBSSO_ENABLED = True
 # Do not remove the mandatory credentials mechanism.
 # Note: The last two tuples are sample mapping keys to a identity provider
 # and federation protocol combination (WEBSSO_IDP_MAPPING).
-WEBSSO_KEYSTONE_URL = "{{ keystone_public_url }}"
+WEBSSO_KEYSTONE_URL = "{{ keystone_public_url }}/v3"
 WEBSSO_CHOICES = (
     ("credentials", _("Keystone Credentials")),
     {% for idp in keystone_identity_providers %}