cope with builds that have "release-google" as hardcoded channel

[bhearsum]

Apparently we shipped something with channel set to release-google-cck-realnetworks at some point (full url is https://aus5.mozilla.org/update/2/Firefox/2.0.0.11/2007112718/WINNT_x86-msvc/ja/release-google-cck-realnetworks/Windows_NT%205.1/update.xml). These builds currently get exceptions when trying to update, eg:

KeyError: 'release-google'
  File "flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "connexion/decorators/decorator.py", line 66, in wrapper
    response = function(request)
  File "connexion/decorators/validation.py", line 293, in wrapper
    return function(request)
  File "connexion/decorators/produces.py", line 38, in wrapper
    response = function(request)
  File "connexion/decorators/response.py", line 85, in wrapper
    response = function(request)
  File "connexion/decorators/decorator.py", line 42, in wrapper
    response = function(request)
  File "connexion/decorators/parameter.py", line 195, in wrapper
    return function(**kwargs)
  File "auslib/web/public/client.py", line 126, in get_update_blob
    app.config["SPECIAL_FORCE_HOSTS"]))
  File "auslib/blobs/apprelease.py", line 166, in getInnerXML
    patches = self._getPatchesXML(localeData, updateQuery, whitelistedDomains, specialForceHosts)
  File "auslib/blobs/apprelease.py", line 279, in _getPatchesXML
    xml = self._getSpecificPatchXML(patchKey, patchKey, patch, updateQuery, whitelistedDomains, specialForceHosts)
  File "auslib/blobs/apprelease.py", line 97, in _getSpecificPatchXML
    url = self._getUrl(updateQuery, patchKey, patch, specialForceHosts)
  File "auslib/blobs/apprelease.py", line 248, in _getUrl
    url = self['fileUrls'][getFallbackChannel(updateQuery['channel'])]

Probably the simplest thing to do is to add "release-google" to whichever blob is serving updates for them.

(Imported from https://bugzilla.mozilla.org/show_bug.cgi?id=1379281)