Move horizon apache root to /dashboard

With keystone's move to /identity, a conflict in for resources was
created as both keystone and horizon used /identity. The keystone
config took precedence and rendered API output in the horizon UI.

This patch sets the root for horizon to /dashboard and serves all
horizon content from there. Additionally, a RedirectMatch has been added
to the apache config for horizon to redirect '/' to '/dashboard' this
will allow the implementation to change without being immediately
painful to users.

Also made the path '/dashboard/' configurable in stackrc.

Closes-Bug: #1478306
Depends-On: I9a04f936ed6d8c14775a332dc28e903992806c42

for devstack-gate changes to remove hard coded horizon url structure
assumptions.

Change-Id: I6fbca5cea9e44df160afbccc71bd045437657320
diff --git a/files/apache-horizon.template b/files/apache-horizon.template
index 6883898..bfd7567 100644
--- a/files/apache-horizon.template
+++ b/files/apache-horizon.template
@@ -1,5 +1,5 @@
 <VirtualHost *:80>
-    WSGIScriptAlias / %HORIZON_DIR%/openstack_dashboard/wsgi/django.wsgi
+    WSGIScriptAlias %WEBROOT% %HORIZON_DIR%/openstack_dashboard/wsgi/django.wsgi
     WSGIDaemonProcess horizon user=%USER% group=%GROUP% processes=3 threads=10 home=%HORIZON_DIR% display-name=%{GROUP}
     WSGIApplicationGroup %{GLOBAL}
 
@@ -8,7 +8,10 @@
     WSGIProcessGroup horizon
 
     DocumentRoot %HORIZON_DIR%/.blackhole/
-    Alias /media %HORIZON_DIR%/openstack_dashboard/static
+    Alias %WEBROOT%/media %HORIZON_DIR%/openstack_dashboard/static
+    Alias %WEBROOT%/static %HORIZON_DIR%/static
+
+    RedirectMatch "^/$" "%WEBROOT%/"
 
     <Directory />
         Options FollowSymLinks