Minor tweaks to retry utility

src/ci/shared.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/false
 # Copyright 2016 The Rust Project Developers. See the COPYRIGHT
 # file at the top-level directory of this distribution and at
 # http://rust-lang.org/COPYRIGHT.
@@ -9,13 +9,16 @@
 # option. This file may not be copied, modified, or distributed
 # except according to those terms.
 
+# This file is intended to be sourced with `. shared.sh` or
+# `source shared.sh`, hence the invalid shebang and not being
+# marked as an executable file in git.
+
 # See http://unix.stackexchange.com/questions/82598
 function retry {
+  echo "Attempting with retry:" "$@"
   local n=1
   local max=5
-  local delay=15
   while true; do
-    echo "Attempting:" "$@"
     "$@" && break || {
       if [[ $n -lt $max ]]; then
         ((n++))