This prevents --no_auth from always clearing BOTO_CONFIG, since there
are times when a BOTO is needed for other things than just auth info
(e.g. proxy settings).

BUG=443523
R=hinoka@chromium.org, szager@chromium.org

Review URL: https://codereview.chromium.org/844373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@293652 0039d316-1c4b-4281-b951-d872f2087c98