Correct var name in globals.yml

Change variable name ceph_use_cache to ceph_enable_cache

TrivialFix

Change-Id: Ifeabf2a7212a78a81703f3e867c2566652b1aebc

etc/kolla/globals.yml

@@ -103,7 +103,7 @@ neutron_external_interface: "eth1"
 ###################
 # Ceph can be setup with a caching to improve performance. To use the cache you
 # must provide separate disks than those for the OSDs
-# ceph_use_cache: "no"
+#ceph_enable_cache: "no"
 # Valid options are [ forward, none, writeback ]
 #ceph_cache_mode: "writeback"