dashboard: move key.py out of the way,

so that if you have a key.py with the real key,
there is no chance hg change will accidentally
make a CL with the real key and upload it to codereview.

R=agl1
CC=golang-dev
https://golang.org/cl/196051

misc/dashboard/godashboard/key.py → misc/dashboard/godashboard/key.py.dummy

@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
+# Copy this file to key.py after substituting the real key.
+
 # accessKey controls private access to the build server (i.e. to record new
 # builds). It's tranmitted in the clear but, given the low value of the target,
 # this should be sufficient.