We missed to refactor CephExternal when migrating to the new
hiera hook. The old template would have pushed the value of
ceph::profile::params::client_keys as a string causing the
deployment to fail with:
Error while evaluating a Function Call, {...} is not a Hash
The new template emits that same data as a map, as it happened
for the other services in Ibe7e2044e200e2c947223286fdf4fd5bcf98c2e1
Change-Id: I3cf59b7d8343d7433047e9ccef310d287dbd47b5