validate: add a check for nfs standalone

if `nfs_obj_gw` is True when deploying an internal ganesha with an
external ceph cluster, `ceph_nfs_rgw_access_key` and
`ceph_nfs_rgw_secret_key` must be provided so the
ganesha configuration file can be generated.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 003aeea45a)

roles/ceph-validate/tasks/check_nfs.yml

@@ -0,0 +1,8 @@
+---
+- name: fail if ceph_nfs_rgw_access_key or ceph_nfs_rgw_secret_key are undefined (nfs standalone)
+  fail:
+    msg: "ceph_nfs_rgw_access_key and ceph_nfs_rgw_secret_key must be set if nfs_obj_gw is True"
+  when:
+    - nfs_obj_gw
+    - groups.get(mon_group_name, []) | length == 0
+    - (ceph_nfs_rgw_access_key is undefined or ceph_nfs_rgw_secret_key is undefined)

roles/ceph-validate/tasks/main.yml

@@ -101,3 +101,7 @@
   when:
     - radosgw_frontend_type == 'civetweb'
     - radosgw_civetweb_num_threads is defined
+
+- name: include check_nfs.yml
+  include_tasks: check_nfs.yml
+  when: inventory_hostname in groups.get(nfs_group_name, [])