btl/tcp: add show_help message when peer hangs up

We commonly see messages on the users list where a peer has hung up
because it has crashed.  Instead of having just a BTL_ERROR message,
make this a real opal_show_help() message that tells the user that the
peer unexpectedly hung up, and they should look into *why* that peer
hung up.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

opal/mca/btl/tcp/btl_tcp_frag.c

@@ -14,7 +14,7 @@
  *                         reserved.
  * Copyright (c) 2015      Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
- * Copyright (c) 2015 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2015-2016 Cisco Systems, Inc.  All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -44,8 +44,12 @@
 
 #include "opal/opal_socket_errno.h"
 #include "opal/mca/btl/base/btl_base_error.h"
+#include "opal/util/show_help.h"
+
 #include "btl_tcp_frag.h"
 #include "btl_tcp_endpoint.h"
+#include "btl_tcp_proc.h"
+
 
 static void mca_btl_tcp_frag_eager_constructor(mca_btl_tcp_frag_t* frag)
 {
@@ -225,6 +229,16 @@ bool mca_btl_tcp_frag_recv(mca_btl_tcp_frag_t* frag, int sd)
             btl_endpoint->endpoint_state = MCA_BTL_TCP_FAILED;
             mca_btl_tcp_endpoint_close(btl_endpoint);
             return false;
+
+        case ECONNRESET:
+            opal_show_help("help-mpi-btl-tcp.txt", "peer hung up",
+                           true, opal_process_info.nodename,
+                           getpid(),
+                           btl_endpoint->endpoint_proc->proc_opal->proc_hostname);
+            btl_endpoint->endpoint_state = MCA_BTL_TCP_FAILED;
+            mca_btl_tcp_endpoint_close(btl_endpoint);
+            return false;
+
         default:
             BTL_ERROR(("mca_btl_tcp_frag_recv: readv failed: %s (%d)",
                        strerror(opal_socket_errno),

opal/mca/btl/tcp/help-mpi-btl-tcp.txt

@@ -74,3 +74,20 @@ Fall back to the normal progress.
   Local host: %s
   Value:      %s
   Message:    %s
+#
+[peer hung up]
+An MPI communication peer process has unexpectedly disconnected.  This
+usually indicates a failure in the peer process (e.g., a crash or
+otherwise exiting without calling MPI_FINALIZE first).
+
+Although this local MPI process will likely now behave unpredictably
+(it may even hang or crash), the root cause of this problem is the
+failure of the peer -- that is what you need to investigate.  For
+example, there may be a core file that you can examine.  More
+generally: such peer hangups are frequently caused by application bugs
+or other external events.
+
+  Local host: %s
+  Local PID:  %d
+  Peer host:  %s
+#