duplicate time series in server-traces

[rcarpa]

Motivation

Internal Error
Duplicated timeseries in CollectorRegistry: {'rucio_trace_trace_total', 'rucio_trace_trace', 'rucio_trace_trace_created'}
  File "/usr/local/lib/python3.6/site-packages/rucio/web/rest/flaskapi/v1/common.py", line 54, in dispatch_request
    return super(ErrorHandlingMethodView, self).dispatch_request(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/flask/views.py", line 158, in dispatch_request
    return current_app.ensure_sync(meth)(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/rucio/web/rest/flaskapi/v1/traces.py", line 67, in post
    trace(payload=payload)
  File "/usr/local/lib/python3.6/site-packages/rucio/core/trace.py", line 301, in trace
    record_counter('trace.trace')
  File "/usr/local/lib/python3.6/site-packages/rucio/core/monitor.py", line 213, in record_counter
    COUNTERS[name] = counter = MultiCounter(statsd=name, labelnames=labels.keys() if labels else ())
  File "/usr/local/lib/python3.6/site-packages/rucio/core/monitor.py", line 153, in __init__
    self._prom = self.init_prometheus_metric(prom, self._documentation, labelnames=labelnames)
  File "/usr/local/lib/python3.6/site-packages/rucio/core/monitor.py", line 179, in init_prometheus_metric
    return Counter(name, documentation, labelnames=labelnames, registry=self._registry)
  File "/usr/local/lib/python3.6/site-packages/prometheus_client/metrics.py", line 134, in __init__
    registry.register(self)
  File "/usr/local/lib/python3.6/site-packages/prometheus_client/registry.py", line 31, in register
    duplicates))