influxdb_metrics.tasks fails when celery not installed due to unexpected argument `ignore_result`

[realdanurbano]

If one does not have celery installed, the function write_points in influxdb_metrics.tasks will fail to load due to the shared_task decorator created locally.

[realdanurbano]

See #37

[dwjorgeb]

This seems to be a very urgent fix, how come it has been almost 2 years without it getting merged?