client: fix pgs num for client pool creation

client: fix pgs num for client pool creation

The `pools` dict defined in `roles/ceph-client/defaults/main.yml`
shouldn't have `{{ ceph_conf_overrides.global.osd_pool_default_pg_num
}}` as default value for `pgs` keys.

For instance, if you want some pools to be created but without explicitely
specifying the pgs for these pools (it means you want to use the
`osd_pool_default_pg_num`), you will be obliged to define
`{{ ceph_conf_overrides.global.osd_pool_default_pg_num }}` anyway while you
wanted to use the current default value already defined in the cluster which is
retrieved early in the playbook and stored in the
`{{ osd_pool_default_pg_num }}` fact.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>