Add oslo::cache to dependency chain

Package installation for cache backend is being migrated to oslo module.
For proper keystone installation dependency sequence should be preserved.

Change-Id: I285cb3ca7e6d6a5d1e6ba68cd12863dca67af151
Closes-Bug: #1756215
(cherry picked from commit 6fd4732471)

manifests/deps.pp

@@ -24,6 +24,10 @@ class heat::deps {
   ~> Service<| tag == 'heat-service' |>
   ~> anchor { 'heat::service::end': }
 
+  # all cache settings should be applied and all packages should be installed
+  # before service startup
+  Oslo::Cache<||> -> Anchor['heat::service::begin']
+
   # all db settings should be applied and all packages should be installed
   # before dbsync starts
   Oslo::Db<||> -> Anchor['heat::dbsync::begin']