VPP-845: add configurable elog post-mortem dump

Off by default. Enable via cmdline "... vlib { elog-post-mortem-dump }
..."

Change-Id: I2056b9de9b37475f2bfeeb5404da838f1b42645a
Signed-off-by: Dave Barach <dave@barachs.net>
diff --git a/src/vlib/unix/main.c b/src/vlib/unix/main.c
index 103576d..e31ea81 100644
--- a/src/vlib/unix/main.c
+++ b/src/vlib/unix/main.c
@@ -409,12 +409,12 @@
 				  format_unformat_error, input);
     }
 
+  error = setup_signal_handlers (um);
+  if (error)
+    return error;
+
   if (!(um->flags & UNIX_FLAG_INTERACTIVE))
     {
-      error = setup_signal_handlers (um);
-      if (error)
-	return error;
-
       openlog (vm->name, LOG_CONS | LOG_PERROR | LOG_PID, LOG_DAEMON);
       clib_error_register_handler (unix_error_handler, um);