Add an alternate default boto file for bootstrapping source.

download_from_google_storage.py

Index: download_from_google_storage.py
===================================================================
--- download_from_google_storage.py	(revision 207434)
+++ download_from_google_storage.py	(working copy)
@@ -238,6 +238,10 @@
   return max_ret_code
 
 
+def ifexists(a):
+  return a if os.path.exists(a) else None
+ 
+
 def main(args):
   usage = ('usage: %prog [options] target\n'
            'Target must be:\n'
@@ -254,7 +258,8 @@
   parser.add_option('-b', '--bucket',
                     help='Google Storage bucket to fetch from.')
   parser.add_option('-e', '--boto',
-                    help='Specify a custom boto file.')
+                    help='Specify a custom boto file.',
+                    default=ifexists(os.path.expanduser('~/.boto.depot_tools')))

[Ryan Tseng, 2013/06/26 17:44:57]

Instead of hardcoding ~/.boto.depot_toos, i'd rather it check for
.boto.depot_tools next to where it would've otherwise found the .boto file, so
that we can put the .boto.depot_tools file in /b/build/site_config/ instead of ~

[Peter Mayo, 2013/06/26 18:20:54]

The .netrc and .ssh configs are in the home directory, so I'm not sure why we
want this one floating elsewhere, but meh.

Also, I'm not sure what uses that as the default, perhaps it isn't deployed yet,
because in my testing on the slave I was given it doesn't work.

[Ryan Tseng, 2013/06/26 19:24:37]

We have some code in run_slave.py that checks to see if theres a .boto file in
<build_dir>/site_config/.boto and use that file if it exists.  This is currently
how all Chromium test bots are configured right now (eg -m1, -m4, etc).

   parser.add_option('-c', '--no_resume', action='store_true',
                     help='Resume download if file is partially downloaded.')
   parser.add_option('-f', '--force', action='store_true',