This does two noticable things:
* Prints a message when "download_from_google_storage --config" is run to
  tell the user to enter "0" for the project ID prompt
* Removes the ".boto.depot_tools" boto file and defaults the boto file to
  grant fullcontrol scopes.

Context: We restricted the depot_tools specific scopes to be readonly out of
concern that we would be forcing every developer to hold a set of non-expiring
write access credentials on their workstation.  But this distinction has caused
a great deal of pain and anguish with confusing credentials (who would've thought
~/.boto.depot_tools would exist and might be broken?), and not for huge security
gains.  Most people don't have write access to buckets, and the ones that do
definitely has a fullcontrol boto file already.

BUG=

Review URL: https://codereview.chromium.org/1182583003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295728 0039d316-1c4b-4281-b951-d872f2087c98