Add enabled check in Backups panel

If enable_backup is False in OPENSTACK_CINDER_FEATURES
then we should not display the backups panel.

Change-Id: I276eebf0f11406bf354f5d8bbecef7b244d6d340
Closes-Bug: #1778771
(cherry picked from commit 6c2225ba)

openstack_dashboard/dashboards/project/backups/panel.py

@@ -14,6 +14,8 @@
 
 from django.utils.translation import ugettext_lazy as _
 
+from openstack_dashboard import api
+
 import horizon
 
 
@@ -25,3 +27,7 @@ class Backups(horizon.Panel):
          'openstack.services.volumev3'),
     )
     policy_rules = (("volume", "backup:get_all"),)
+
+    @staticmethod
+    def can_register():
+        return api.cinder.volume_backup_supported(None)