Respect gcloud analytics opt-out

[bootstraponline]

If a user has opted out of gcloud analytics, disable reporting bugs to bugsnag.

_UUID_FILE_PATH = os.path.expanduser(os.path.join('~',
                                                  '.gsutil/analytics-uuid'))
# If this string is written to analytics-uuid, that means that the user said
# 'no' to analytics, and it should thus be disabled.
_DISABLED_TEXT = 'DISABLED'

https://github.com/bootstraponline/gcloud_cli/blob/41b4d3438d5a8e215912897d2aa615fd8d509e0d/google-cloud-sdk/platform/gsutil/gslib/metrics.py#L55