usnic: add high-verbose reachability messages

(cherry-picked from open-mpi/ompi@87dbe6c)

Author: jsquyres

ompi/mca/btl/usnic/btl_usnic_module.c

@@ -98,11 +98,18 @@ static int add_procs_block_create_endpoints(opal_btl_usnic_module_t *module,
 
         /* Do not create loopback usnic connections */
         if (opal_proc == my_proc) {
+            opal_output_verbose(75, USNIC_OUT,
+                                "btl:usnic:add_procs:%s: not connecting to self",
+                                module->fabric_info->fabric_attr->name);
             continue;
         }
 
         /* usNIC does not support loopback to the same machine */
         if (OPAL_PROC_ON_LOCAL_NODE(opal_proc->proc_flags)) {
+            opal_output_verbose(75, USNIC_OUT,
+                                "btl:usnic:add_procs:%s: not connecting to %s on same server",
+                                module->fabric_info->fabric_attr->name,
+                                usnic_compat_proc_name_print(&opal_proc->proc_name));
             continue;
         }
 
@@ -115,6 +122,11 @@ static int add_procs_block_create_endpoints(opal_btl_usnic_module_t *module,
         if (OPAL_ERR_UNREACH == rc) {
             /* If the peer doesn't have usnic modex info, then we just
                skip it */
+            opal_output_verbose(75, USNIC_OUT,
+                                "btl:usnic:add_procs:%s: peer %s on %s does not have usnic modex info; skipping",
+                                module->fabric_info->fabric_attr->name,
+                                usnic_compat_proc_name_print(&opal_proc->proc_name),
+                                opal_get_proc_hostname(opal_proc));
             continue;
         } else if (OPAL_SUCCESS != rc) {
             return OPAL_ERR_OUT_OF_RESOURCE;