librbd: tweak misleading "image is still primary" error message

m_promotion_state == PROMOTION_STATE_NON_PRIMARY doesn't say anything
about the remote image.  It could still be primary but it could also be
demoted.  Report the status of the local image instead.

Fixes: https://tracker.ceph.com/issues/56676
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

src/librbd/mirror/PromoteRequest.cc

@@ -59,7 +59,8 @@ void PromoteRequest<I>::handle_get_info(int r) {
     finish(-EINVAL);
     return;
   } else if (m_promotion_state == PROMOTION_STATE_NON_PRIMARY && !m_force) {
-    lderr(cct) << "image is still primary within a remote cluster" << dendl;
+    lderr(cct) << "image is non-primary, remote demotion is not propagated yet"
+               << dendl;
     finish(-EBUSY);
     return;
   }