rgw: Better ERANGE error message

Add mon_max_pg_per_osd exceeded as possible cause for ERANGE error

Partially fixes: http://tracker.ceph.com/issues/22351

Signed-off-by: Brad Hubbard <bhubbard@redhat.com>
(cherry picked from commit e35c50c)

src/rgw/rgw_rados.cc

@@ -5777,7 +5777,8 @@ int RGWRados::create_pool(const rgw_pool& pool)
     ldout(cct, 0)
       << __func__
       << " ERROR: librados::Rados::pool_create returned " << cpp_strerror(-ret)
-      << " (this can be due to a pool or placement group misconfiguration, e.g., pg_num < pgp_num)"
+      << " (this can be due to a pool or placement group misconfiguration, e.g."
+      << " pg_num < pgp_num or mon_max_pg_per_osd exceeded)"
       << dendl;
   }
   if (ret < 0)