ceph-dashboard: remove bool filter for rgw vars
ceph-dashboard: remove bool filter for rgw vars

Some dashboard_rgw_api_* variables are using the bool filter but those
variables are strings with an empty string as default value.
So we should test the variable against an empty string instead of a
bool.

dashboard_rgw_api_host: ''
dashboard_rgw_api_port: ''
dashboard_rgw_api_scheme: ''
dashboard_rgw_api_admin_resource: ''

Resolves: #4179

Signed-off-by: Dimitri Savineau <a50a620e679eed14f4e99998b821cea8884cf228@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible