Replace ceilometer central agent by polling agent

central and compute agents were deprecated and have been finally removed
in puppet-ceilometer [1].

[1] https://review.opendev.org/#/c/677428/

Change-Id: Idd491d3a6fd8803682646a8dafb5fe22ad311c71

packstack/puppet/modules/packstack/manifests/ceilometer.pp

@@ -49,7 +49,8 @@ class packstack::ceilometer ()
       auth_region   => hiera('CONFIG_KEYSTONE_REGION'),
     }
 
-    class { '::ceilometer::agent::central':
+    class { '::ceilometer::agent::polling':
+      manage_polling    => true,
       coordination_url => $coordination_url,
     }