[Release] More information on how to close auto-roller

If you are not logged in with your Google account you are
faced with a blank screen. In order to make it more
clear for the Chromium sheriffs on how to close the
auto-roller I want to add this information.

R=machenbach@chromium.org
LOG=N
NOTRY=true

Review URL: https://codereview.chromium.org/1392823004

Cr-Commit-Position: refs/heads/master@{#31670}

tools/release/chromium_roll.py

@@ -17,7 +17,8 @@ ISSUE_MSG = (
 https://code.google.com/p/v8-wiki/wiki/TriagingIssues
 
 Please close rolling in case of a roll revert:
-https://v8-roll.appspot.com/""")
+https://v8-roll.appspot.com/
+This only works with a Google account.""")
 
 class Preparation(Step):
   MESSAGE = "Preparation."

tools/release/test_scripts.py

@@ -989,6 +989,7 @@ https://code.google.com/p/v8-wiki/wiki/TriagingIssues
 
 Please close rolling in case of a roll revert:
 https://v8-roll.appspot.com/
+This only works with a Google account.
 
 TBR=g_name@chromium.org,reviewer@chromium.org"""